Err, most people I know who bought a Wii bought it because of Wii Fit. Perhaps I'm a different demographic to you but it was pretty big when it came out.

The balance board sold 32 million units, so it was a pretty major success. That is as many units as Nintendo64 consoles sold. See http://www.gamesradar.com/holy-crap-look-how-many-wii-balanc...