Wii wins sales hands down.
The issue with the Wii library however is that there are only 2-3 good titles at most every year.
While the PS3 third party titles sell much less, there are enough of them , covering enough genres to catter to the needs of a wide ranges of gamers. That and pretty much every quarter there are 1-2 decent PS3 title released so even if there was no third party support ( which is not the case at all), that is enough for some gamers...
Look at 2010 for example :
MAG
God of War 3
MLB 10 The Show
Modnations Racers
Heavy Rain
GT5
LBP2
On the other hand you get Nintendo with very little third party support that on top of this releases too few good first party titles.
PS3-Xbox360 gap : 1.5 millions and going up in PS3 favor !
PS3-Wii gap : 20 millions and going down !
