People seemed confused about how an N64 title would work on a 360 vs. your Wii. Both are running software-based hardware emulation. I guess Game Cube games run more "natively" then the VC titles, but everything else is exactly the same as running MAME (for example) on your PC. PhoenixUltima is correct that there are legal ways to do this - especially if Rare is so inclinded to modify the game's source to work with the emulation layer they build for the 360.
I wonder if this would really make it less likely to come out for VC? Is there some type of Microsoft arcade eXclusivity (get it? "X"?) for titles?