The big issue Wii will be facing is that same one that brought down the Atari 2600 in its time, the difference is that Nintendo can do something about it whereas Atari coudn't.
Big install base + low development costs = potentially lots of games coming out for the Wii. The issue being that there is actually such a thing as too many games.( average quality go down, customer gets lost among so many titles, good games make less profit..)
What Nintendo needs to do is strenghten their QA and watch more carefully which games they certify. This is not yet an issue on the Wiii, this is starting to be a serious issue for the DS ( seriously how many copies of Brain training are they gonna release ?).
PS3-Xbox360 gap : 1.5 millions and going up in PS3 favor !
PS3-Wii gap : 20 millions and going down !
