Power isn't just graphics. For instance bioware tweeted they couldn't put a holster animation in ME3, because the PS3 lacked enough memory (idk if I buy this but it's what they tweeted!).
also, while gameplay is great... gameplay with great graphics is even better. Artstyle that's great is even better if the graphics are great from a technical perspective too.
If it has worse graphics it needs to have some things that offset it. For instance wii games were cheaper. The controls (though I think this was a negative). The console was cheaper. If the wii-u doesn't have those things, that seems like quite a negative to me.
If all things are equal, having worse graphics and processing power is definetly a ding against it, and I don't know how you can argue otherwise. The idea that games on nintendo consoles are the only consoles with games that have good artstyle or good gameplay is kind of stupid. And they've generally had the worst online as well. And though developers don't take advantage of this a lot, there are gameplay possibilities that only happen with higher processing power.
With all that said, who knows what's going to be the wii-u. It's rumors.
