Sure, mitch and boan yesididthatonpurpose all you like about the Wii, but at least it's more powerful than the Gamecube.
Then why does it keep getting GC ports? Why not make better (looking) games?
Two words:
Lazy developers.
The wii is successful, but not with "core gamers"; it's paradoxically true that the console will fail to attract high sales for games that core gamers want, and as long as the console lacks "core games" core gamers will fail to buy the console (and games for it) in any great numbers.
These "core games" cost more to develop than the games that the wii gets good sales for; therefore, most of any budget is going to go into developing those games. Anything that's left over can be spent on the "core gamers" and therefore this results in...
Sloppy ports!
Not got a lot to do with the console itself, just the market. Quite sad really.