The Wii is more powerful then the original Xbox and the GC, neither of which were ever pushed to the edge of what could be done with it.
Most devs literally use PSP/PS2 type tools and half ass even that, then blame the system for not pushing further. Which I sort of get, but lets be real, it is just them being lazy. Short of games that require intricate AI for multiple characters that would appear on screen at once, there isn't much that shouldn't be possible on the Wii that other games are getting. It is the fact that they'd have to work to reach good graphics and work around the motion controls that turn developers off.
If the Wii2 really did come out and was capable of matching 360 or PS3 level graphics but was slightly deficient in another spec category, devs would claim that and the audience as to why they don't have games on it.