Look at it from another side. Nintendo has already rolled out many of their usual IPs for the Wii: 3D Mario, 2D Mario, Paper Mario, Mario Party, Mario Kart, 2 (Almost) Zeldas, 1-and-a half Metroid Prime game, Smash Bros, Excite (Bike/Truck/Bots) Series, A tie-in Donkey Kong game, a number of Nintendo characters based sports games, even revived Sin and Punishment. But they keep saying they gonna support the Wii for a long time. So I'm pretty sure they have those in the sleeve- F-Zero, Star Fox, Kirby and Pikmin 3, maybe a more platformer-like Donkey Kong (like Jungle Beat). Then this makes sense - in 2010 they release Mario Galaxy 2, Metroid Other M and Zelda. Everyone's happy. And then they live about 2 years off those I mentioned. 5 well-known IPs for 2-3 years- quite all right.
I can't agree about the casual crowd. They can make the actual game rather easy and enable multiple difficulty settings. Or unlockables. Different routes. Different control modes. Online. It's not that difficult. Miyamoto was saying something about making usual IPs accessible and hardcore-appealing at the same time. Worked pretty good for Mario Kart, NSMB, MP3: Corruption, SSBB.