Whenever I hear people say they like playing on a Wii, usually the only game I hear them talk about is Wii Sports. And they're usually not the 15-25 (or whatever the heck it is) year old crowd either. I've heard relatively few people mention playing other games. Take my sister for instance. She keeps telling me how the bowling, tennis, and baseball events are really fun and wishes she had a Wii. I then asked her what other games she's played, and she said none because her friend only had Wii Sports.
I think people bought the system for the innovative control, and the game was made to show how they can be implemented. Wii Sports is selling well because it's packed in and because it lets you use the Wiimote. It recieved average scores from the press yet it's in the top ten of best-sellers. The good sales could also be attributed to the fact that it has relatively few good games (in terms of scores).
On another note, the Japanese have been in a quirky game craze these past two years. That's why the Wii and DS are so popular there. Nintendo's bringing it to the U.S. now with mainly just this game.
