I'm sorry, I stopped reading when you said "Let's not forget Sonic and Bonk will both be taking sales away from our favorite plumber." I think they tried that before, a few times each actually. Now they both make Nintendo games. Nintendo eats its competitors.
Buying a Wii without buying a 4-player 2-D Mario game is going to be as hard as buying a SNES without Super Mario World. Yeah, in both cases it's physically possible, but not too many people can actually do it.