The thing of it is, the Wii gets criticized because the hardware isn't as powerful as the Playstation 3 or the Xbox 360. While that may be (is) true, the big deal here is that Nintendo has stepped up, took a BIG risk by sacrificing HD graphics with their next generation system, and tried something different.
It just so happens that people like the Wii, despite the fact that it doesn't have the best graphics capabilities. It proves that gameplay IS a LOT more than people previously believed. The Wii is selling out around here, whereas there are PS3s available for purchase, sitting on store shelves.
That says 3 things:
1. Graphics aren't everything.
2. Gameplay means something.