Hey, I'm all for mixing fun and physical activity. Active games are good. I don't have a wii but I'd kinda like one. DDR is fun to play.
But who thought banning fat people from playing video games was a sensible thing to do?? Even if you somehow believe that with the entire world telling them how much they suck, this one detail is going to magically make them thin again, a) what business sense does it make to implement a feature designed to annoy your playerbase and b) why would people agree to input the data required to disable the games they want to play?
I suppose if they aim it at children, over-controlling parents might enjoy that.