I'll try to explain a few things to you.
The Super Nintendo was the RPG king, but what RPGs did the N64 have? Pretty much all the RPGs were on PlayStation and Saturn. RPGs don't always align with the same console company, ever.
I've said this many times, part of what helped MS is they released 360 development kits at a perfect time, before Sony got out to these developers. They gave Tales Studio, Tri-Cresendo, Tri-Ace, etc. development kits just as they finished their previous RPGs (or Tri-Cresendo about started to make their first independently developed RPG). These devs had a choice of developing on PS2 or 360. Since many were already sick of developing on PS2, they went 360. Since the 360 wasn't out, they couldn't tell if it was going to be a success or failure. So they went ahead and made 360 projects. Mistwalker was already planning on making games for Xbox platforms since he was planning that all along (partially because of his shaky relationship with people at Sony). MS did heavily fund Infinite Indiscovery initially (Tri-Ace RPG), but then handed publishing to Square Enix (figuring they could probably sell more). As much as I don't want to believe this, I honestly won't be surprised if Star Ocean 4 ends up on 360, since Tri-Ace's next gen engine was made on 360 (and there was talk they had another 360 RPG coming due to a job posting). But basically, what helped MS a lot was coming in early. Most every time in Japan, the console which comes first, will always get some decent RPGs (despite the Dreamcast not lasting long, it even got a few decent RPGs due to being first). I also think that MS probably paid these devs too to keep these RPGs on 360 (at least as a timed exclusive), like for ToV.
Devs like Idea Factory though, they make RPGs for just about everything (mediocre ones too). They've released around 2 PS3 RPGs (have a few in development, one is Cross Edge), 2-3 360 RPGs, and in the past, they even released an Xbox RPG unlike most.
As for Sony, I'll just basically say during the PS1 era, they were pretty big RPG developers. The had G-Craft making Arc The Lad (big success in Japan), PoPoLoCrois (sold well), Wild Arms by Media Vision (sold well), Alundra by Matrix Software (sold good I believe), Legend of Dragoon (performed excellent worldwide), Legend of Legaia (by Contrail and sold good) Beyond the Beyond by Camelot (not sure how it did), and so on.
However, during the PS2 era, many of these series did not carry on with the sales. Legend of Dragoon team is no longer together (I remember a few of its devs were apart of MS Japan, but then it disbanded and is kind of AQ now). PoPoLoCrois, Legaia, Matrix software's PS2 RPG Dual Hearts, Arc The Lad games on PS2 (made by Cattle Call instead, since G-Craft is absorbed in Square Enix making Front Mission games), Legaia 2, etc. all performed pretty bad (where they may have lost money in development due to pretty bad sales). New RPGs they tried to make like Tsugunai, Okage The Shadow King, etc. bombed badly too. Their only successes came from Level 5 (well, not really huge success since Rogue Galaxy and Dark Cloud 2 sold less than expected, but still did pretty good overall) and somewhat Wild Arms (the series dropped in sales, but still did solid). Many of the devs Sony worked with, like Matrix Software, are elsewhere (Matrix is working on remaking FF games on DS for Square Enix, I have no idea where Contrail and Cattle Call are now), and Camelot is Nintendo exclusive basically. So mostly, Sony themselves just stick to Level 5 RPGs and Wild Arms. They do have Game Republic (who made Folklore on PS3 and Brave Story on PSP) and Gaia (who made Monster Kingdom and Coded Soul. Made up of the original SMT creator), but their traditional RPGs have gone to PSP (and future projects may stick to PSP). Media Vision (makers of Wild Arms) just finished Wild Arms 5 around the same time PS3 came out in Japan (they released another PS2 Wild Arms so it would happen around the 10th Anniversary for the series. Wild Arms XF came out in 8/9/07 in Japan (PSP WA game).
So IF Media Vision were to make a PS3 Wild Arms game (Sony does not own them, and if they rather make a Wii game, they can), it would not come out until late 2009 at the earliest, since they gotta develop a graphic engine for PS3 and it will be their first time developing on PS3. Level 5 will continue to make PS3 RPGs and everyone can rest assured (unless something shocking happens) they'll mostly stick to PS3 when it comes to consoles (They have a pretty bad relationship with MS over the canceling of True Fantasy Live Online). Level 5 has been awfully quiet on everything lately (we only know of White Knight Story and DQIX coming to DS by them, but they haven't given any updates on them). I do feel once WKS is released, they'll reveal their next PS3 RPG (rumored to be Dark Cloud 3 or Rogue Galaxy 2). Those are the only RPGs I see coming from SCEJ themselves, since developing on PS3 is a bit costly and if the game bombs (which is very likely since they really don't have any quality RPG devs outside of Level 5 and Media Vision), they'll lose more money (and Sony is already losing money on PS3). And then, you have to hope SCEA brings them stateside, because SCEA already isn't too fond on bringing RPGs stateside since many of them just won't sell stateside (I know someone within SCE Santa Monica who mentioned Folklore almost didn't come stateside because of what SCEA felt, but someone within convinced them to bring it over. And it MIGHT explain why we didn't get Dark Mist). But SCEA is good and allows other publishers to release their stuff stateside (unlike Namco).
Now for the third party situation, Sony has usually been pretty lucky to receive an RPG from Capcom, Konami, etc., with several from Namco, Bandai, ATLUS, Square, Enix, Banpresto, some from Sega, and other devs. Capcom doesn't make RPGs anymore (Breath of Fire V really bombed and Mega Man X: CM didn't do so great. The only kind of RPGs they make are Mega Man Starforce games on DS). Konami still has Suikoden, but with the massive downsizing Konami has done (outsourcing many of those games) who knows when it will come (I'm predicting it will come to Wii, since Suikoden isn't a high budget RPG and Konami is mostly sticking to Wii). Namco, who knows with them, because they did have 360 development kits early which explains why 360 got a few RPGs early, but they're giving PS3 crap support mostly and seem to favor 360. We haven't heard them announce a new PS3 RPG yet, outside of an Eternal Sonata port which is coming sometime. Bandai hasn't really made a next gen RPG yet, but there's a chance CyberConnect2 (makers of .hack) will make a PS3 RPG since they are working on Naruto: Ultimate Ninja Storm on PS3 (so they have a graphic engine made on PS3). ATLUS is still stuck to making last gen games (Persona 4 is coming out soon to PS2, since they opted to stay PS2 then go 360). They have said many times they will make a PS3 SMT game, so we'll see. SMT3 (the first ATLUS PS2 RPG developed) didn't come until 2/20/03 (almost 3 years after the PS2 was out in Japan, and PS3 hasn't even been out two years in Japan). Square Enix hasn't really done much for next gen. All they have on 360 so far is publishing IU and LR is multi-platform (FFXI was an old port). On PS3, they have FFXIII, FF Versus XIII, and LR. But at the moment, Square Enix is mostly developing on handhelds, since Wada is all profit and DS prints lots of money. Reason why PS2 got FFX early was because Square was originally almost 2nd party to Sony and assured PS2 got FFX in a good time frame. Wada (who was mostly Enix before and only cares about profit) could careless when PS3 gets FFXIII, so he isn't going to try pushing the game out quicker (it's being said he's holding development back since DQIX isn't out yet and he wants more PS3 consoles to be sold). Most Banpresto games are Japan only, but I see most going to handhelds if anything. Sega has brought Valkyrie Chronicles to PS3. They haven't brought any RPGs to 360, and I think they'll bring more PS3 RPGs (but most will be Wii/DS). Who knows about the Shining series, but Shining Tears might happen on PS3 (since the devs also make Yakuza).
What does hurt Sony a bit more than some of you have thought is, PS2 say three Xenosaga games, but now Monolith Soft is owned by Nintendo, so the series is done. There were three Shadow Hearts games on PS2, but since the developer was dissolved, there goes that series (some of them are with Feel Plus, who mostly works with Mistwalker). The Tales series and others probably won't see as many installments, and some may end up on handhelds.
Some good news is, NIS will develop PS3 SRPGs, Gust has a PS3 RPG coming (as long as they don't cancel it), and Square Enix should be bringing RPGs to PS3 (they said Wii, DS, and PS3 will get the bulk of their games).
Overall, there's no denying PS3 will see very few RPGs this generation because:
-360 came out earlier, got some of the developers before PS3. MS has very deep pockets to keep games on their platforms.
-RPGs tend to go to the console with the larger userbase in Japan, and the Wii has it.
-Handhelds are a bigger success this time, which is why DS/PSP are even taking some RPGs away from consoles now.
-PS3 is just really expensive and complicated to develop for. Valkyria Chronicles had to sell 500k copies to break even due to the graphic engine they invested in. The game sold 120k in Japan, and I really doubt it will sell 380k in NA/Europe. Being expensive and complicated does kind of scare devs away from making an investment to make games on it (western devs who make multi-platform games isn't bad, because making a PS3/360 game costs around the same as a PS3 exclusive). SCEJ is more likely to make PSP RPGs if they make an RPG since the PSP is doing very well in Japan and development cost is much lower.
When thinking about it, PS3 and 360 are in-line when it comes to RPGs stateside. All 360 got in its first year was Enchanted Arms (PS3 got that and Folklore). 360 in its 2nd year got Eternal Sonata and Blue Dragon, while PS3 gets Disgaea 3 and Valkyria Chronicles. 360 gets Culdcept Saga (kind of RPG), Lost Odyssey, Operation of Darkness (terrible game, but still), Spectral Force 3 (I doubt it will be good), IU, and ToV tis year. If PS3 gets 6 RPGs in 2009 (very possible IMO), 360 and PS3 will be on the same pace basically. I just think people expected no RPGs on 360, while PS3 gets all the RPGs, but they are looking to be about the same, just that 360 looks better due to a year headstart.
Well, that's all I'm going to say. If you really want RPGs, buy a DS, that's my suggestion (It gets too many awesome ones this year). I think 360 will have the RPGs in the short term, but in the long term, it's up in the air (Because FFXIII are the biggest RPGs to come, while I expect 360 to see a dip in RPGs later on but has a decent number now, and Wii is doing very well and may get a lot). If someone wants RPGs now on a console, just buy a 360 and not worry about waiting for PS3 to get them.
If PS3 fans want more RPGs, I highly recommend buying Disgaea 3 and Valkyria Chronicles (which is a VERY good game I hear too) when they come out, because if they sell well, we should see more.
I made this long posts because I'm getting tired of hearing this argument from PS3 fans. RPGs do NOT follow just one manufacturer unless Square Enix was making a game console. Do NOT assume one consoles has the RPGs until you see announcements or they are released.
EDIT: Yes, having the PS2 still around hurts, because some devs are still making RPGs for PS2. One reason MS killed off Xbox so quickly was so ALL devs would move to 360. Sony kind of needs to do it, but at the same time, Sony needs PS2 so they can lessen loses on PS3.
White Knight Story is not Vaporware. Level 5 has just been quiet about everything they've been making as of late. It will come, we just don't know when.