The Wii doesn't apear to have the same lifepsan as the PS2 , in it's first couple of years Nintnedo have brought out all their major first party titles Mario Galaxy,Kart,Zelda,WiiPlay,Wii Fit etc. I don't think they could keep that up for another 6 years.
Plus the casual market is unpredictable , i'd guess they're always looking for newer,innovative and different ways to have fun . Will the Wii remain the casual's choice for years to come ? I'm not so sure.
3rd Parties will keep the Wii going that's for sure.










