In response to remarks from Steven Kent to USA Today predicting an upcoming Wii bubble burst-- an end to its massive popularity, brought on by a high price relative to its power, Game|Life's Chris Kohler wrote a brilliant editorial looking at what he sees as the four different kinds of gamers (in terms of casual-to-hardcore) and how such a bubble burst would affect them.
Most interestingly, Kohler defines the "casual gamer" not as we do now (non-gamers who enjoy some Bejeweled) but as the majority of the gaming public who buys systems following price drops and owns two or three games. The grandmas and such fit into the "expanded audience." The other two categories, "hardcore gamer" and "kid" are much easier to define.
In Kohler's view, the only audience whose interest in the Wii would be affected by a "bubble burst" would be the casual gamers, who may be more willing to respond to an Xbox 360 price drop than an underpowered Wii. Unless, of course, the Wii gets a bunch of mass-market games.