I don't see the worry, I admit, the screens shown are pretty bad, but if you look at MP3 screens you can see that the Wii is capable of a lot better, even so, it's the fresh ideas and gameplay that make me buy something more than just the flashy graphics. Games that are aeons old are still great fun for me, even if they graphics are terrible. Not that I'm saying the Wii has terrible graphics...as I said above, looking at screens from other games show that the Wii is capable of good things.
And like someone above said, which has always decided my mind for me, any game I see on the XBox that looks good I just wait a little while and buy on the PC, as for Sony...well...there's no chance of me buying something of that bunch of money hungry theives.