It depends on what you mean by casual gamers, but overall, I pretty much agree with the OP. I'd say that Wii owners are buying more "casual" titles than they did before. Look at the Wii's top sellers this year.
1. Just Dance 3 (1713k)
2. Zumba Fitness (1159k)
3. Mario Party 9 (1091k)
4. Zumba Fitness 2 (940k)
5. Mario Kart Wii (798k)
6. NSMB Wii (783k)
And the list is games like those down to Skyward Sword at 10th. In other words, there's absolutely nothing to suggest that the Wii owners now buy more "hardcore" titles than they did before.
Similarly, there's nothing to suggest that Wii owners are buying noticeably fewer games than they did before. There are fewer games bought due to fewer consoles bought, but I'm personally surprised at how well the Wii's software sales are holding up.
