I don't want a PS3 now, but I'm sure I will eventually when I see good games out for the system - the reason I bought a PS2 was for the RPGs (like Final Fantasy). I don't want one out of brand loyalty - if anything I'm a Nintendo fangirl, and I want a Wii for the awesome games that I've heard of (and there are a lot) - but because I'm sure there will be good games soon.
As for why don't I want a 360? Actually, hearing about the games kinda makes me want one. I'll admit I'm a little biased without reason on the whole Microsoft thing, but... I can't stand the controller. It feels as awkward as the NES one in a different way. Also, the original X-Box had very few games that appealed to me, and I'm not sure the 360 is any different - but who knows, maybe it will be.
Graphics are nice and all, but a game with good graphics and no plot, no gameplay, and no... fun is just images. As long as the graphics are decent for the system, I'm happy (that is, no N64-worthy graphics. I'll never get those standing-through-a-wall images out of my head).