I will tell you exactly why Konami has not made a PS3 DDR: It isn't worth it.
Konami has already established a large niche market with PS2 DDR releases over the years. The PS3 has a significantly smaller userbase and it isn't one that lends itself so freely to dancing sims in comparison to still-popular PS2. Continuing PS2 DDR means they don't have to worry about stale sales from catering to a console less people own, they don't have to create a new line of DDR pads for the wireless PS3, and they also don't have to worry if there's enough of DDR buyers who made the leap to PS3. And perhaps the biggest reason is that a PS2 release still reaches out to some PS3 owners due to backwards compatibility (the USB-to-PS2 controller port works for DDR pads). The sum total of these reasons place PS2 as both the most cost-efficient choice and the stage with the most possible DDR buyers.
Aside from audience precision, another reason is that PS3 DDR would not change in any crucial way from PS2 DDR. Technical-wise, the DDR games have no real reason to go to PS3 to begin with. There is really no advantage to having HD 1080p DDR or higher-polygon dancers because the player is only going to be concerned about the arrows, gameplay-wise, and anything else is already performed well-enough by the PS2. The only crucial factors in DDR are that the arrows are displayed clearly, the audio quality is good, the background animations are decently mesmerizing, that the arrows run at a smooth framerate, and perhaps an online component. The arrows are simple graphic skins, so they need no graphical overhaul. The audio is already at a good quality. The background animations are also simplistic in that colorful animations/designs are capable through simple graphics rendering that even PS2 can do. The animations have also incorporated music videos for licensed songs lately, and PS2 is capable of even this and with efficient clarity. The current framerate of DDR is already incredibly smooth and effective for all difficulty levels and arrow-scroll speeds. And for online component, 3 PS2 DDR games have already done that.
DDR won't even benefit being on a Blu-Ray disc. The traditional 70-something total songlist doesn't even come close to occupying the majority of a DVD. In fact, the total data size of a DDR game is far less than the typical PS2 game (which may even be why most PS2 DDR games debut at $10 cheaper). The only reason Konami keeps to the same amount of total songs in a game is because, like someone else said, it meets the level of demand. Konami recycles the right amount of old songs and backs them up with the right amount of new songs in each DDR game so they don't have to produce/license any more new songs than they need to.
The only reasons DDR would have enough reason to go to PS3 is if there is enough demand or potential exploit for PSN online play. However, there isn't really any demand for it yet, and it doesn't help that DDR is a party game anyhow (encouraged by many to be played with others in the same room). I think if PSN evolves into a large-enough, robust community, we may see Konami bring DDR to PS3 in order to tap into that community (a tried-and-true party game would naturally be warmly welcomed by a large community), but right now it simply isn't worth it.
It will come out in September, like usual.
