I think what you may want to look at differently is what downloadable content is available. Also, I'm pretty sure songs from Rock Band 1 are compatible with 2, the downloadable songs. That is what I would really care about and I think for the time being Rock Band wins that fight.
I would be gun shy about Guitar hero based on the other ones I own and played. Most of the songs I didn't recognize or totally never heard of, most of the songs were not my type of song, for me being a fan of rock and roll, heavy metal, etc. Rock Band suits me more..in my opinion anyway. But that's going to change when Guitar Hero Metallic is released. I absolutely cannot wait for that game.
I've always liked Sonys stuff, in general. But I really have no desire for the PS3. My PS2 sits dormant, as it really has since I've owned it. I've had mine since a few months after launch and I only have 8 titles for it, it never got played. My PSP I absolutely love, but I tend to play portables more than consoles as for my situation it's just easier. When Barney the big purple dino is on tv, i'm on my psp. The 360 really has been the first system since the SNES to give me that WOW factor, i'm sure the PS3 is the same way for people that just have the 360. The Wii has absolutely no wow factor. I'm not saying it's not fun, you can see my reviews. The games I've had I really like, but the system itself is what does it for me, especially when I have a 360 and a Wii, it's a no brainer. They are truly for 2 totally different types of gamers.
I might be interested in a new Wii depending on the games. #1. I don't want rehashes. #2 I don't want cute and cuddely, #3. I'm burned out on the same old Nintendo franchises. #4. I want waay better online service. #5 I want games like Assassins Creed, Gears of War, Oblivion, Dead Space, Socom, GTA, Bioshock, Mass Effect, not saying these games exactly, but games like them. And honestly, what would make me believe the software side would change. Xbox 720 and PS4 is probably still going to be the way to go for these types of games.
I think Nintendo may have the hardest time following up. Catering to the non-gamer crowd, they really need to give consumers a reason to stop with the Wii and move on, if the games are the same old same old, they may be less reluctant to do so as graphical and technical enhancements probably aren't going to matter as much to casual gamers.
Its still rumors and frankly, I think both systems would have more life in them to last longer than 2010. Though it would make more sense for Nintendo. by 2010 there should be a lot more people with HD Tv's, people might be screaming for a hard drive, by 2010, maybe Nintendo will have a comparable machine in the market.