So with the PS4 not being backwards compatible (last I heard - and not counting the "streaming" of which I remain skeptical) here's another reason why I had no qualms getting a Wii U at launch and yet will be hesitant to get a PS4 or Nextbox.
I knew that with the Wii U I'd be able to play nearly all of my old Wii content without the need for leaving the Wii hooked up. In fact, I could "upgrade" and get rid of my old Wii in the process. I haven't actually done that yet but given that it is a GC-compatible one I ought to be able to get $60-$75 for it.
With the PS4 (and probably Nextbox as well), I'll have to hold on to those old systems for sure. And we actually have 2 of each and I'll feel like I'll need to keep both (for the various kids). If their next systems were going to have BC I'd feel confidant getting rid of at least one soon and then getting the new system at launch. But as it is I will try to hold off. Unfortunately, my 360 fanboy son will probably want the next Xbox ASAP and I might not be able to avoid that purchase (as much as I would like to).
And sure, I tend to be in the camp of those who downplay backwards compatibility. After all, I still have the old reliable Gamecube hooked up so I never once played a GC game on the Wii. And I still have my PS2 hooked up but haven't used it in at least 3-4 years. But knowing that I won't be all that interested in most of the launch titles for either new system I figured older games will still get most of the playtime for the first couple of years (I didn't get either the 360 or PS3 at launch as I still had lots to play). But, for example, just today I needed to bust out Epic Mickey because my 5 year-old saw the newer game in the store this evening and wanted to play. It was easy as pie to put that in the Wii U and spin it up. Had the Wii U not had that capability I probably wouldn't have bothered (nor would I probably even have a Wii U now).
It is a small thing, but something Nintendo does right in any case.
(And note that I said "nearly all" of my Wii content because it appears the Wii Shop game "Lost Winds" did not transfer nor is available in my previous downloads on the Wii Shop. I was redownloading those games in preparation for the Wii U upgrade program and all the ones that were on the SD card as opposed to the Wii internal memory would not play until I redownloaded them).