It's possible the Wii could maintain the momentum it's had however the casual market isn't as predictable as the "hardcore" market , you can almost guarantee GTA's Final Fantasy's will sell in millions .
The thing about casual gamers is that they're not loyal to any one device or brand , they'll switch to the next big thing w/o hesitation. You'll notice in any market experience growth like the "casual gamers" market the Wii is almost guaranteed to face new competition which will take away from it's market share.
Edit : I could give in to Wii selling around 35 mill this year with sufficient reasoning however 105 Mill by the end of it's gen. You can quote me on this when I say it's impossible for the Wii to achieve PS2 sales, the PS2 grabbed the majority of every gaming market Hardcore and casual alike for the majority of it's lifespan .
