that is simply nmot true.
12 out of the 23 million sellers for wii (not including wii play/sports) are hardcore games. thats more than the half. only 2!!! are casual games and the rest are party games.

sure, there are alot of casual games on the wii, but there are also alot of hardcore games that simply and plain just suck.

a complete list reveals more hardcore games than casual games, and also alot of party games.

source: VGChartz.com, wikipedia list of wii games