Yea, it really is ridiculous that we are having this conversation and people again and again are missing three very vital and important points.
First, the wii is less than one year old. Does anyone realize that? Almost never do the console defining games come out in the first year of the release. (NES-SMB3, SNES-Donkey Kong Coutnry/Mario World, PS2-Grand theft auto series). It just doesn't happen that way, game developers need to work with a console for a while, especially one with motion sensing, and get used to it.
Second, the wii is doing incredibly well in sales. Do not compare this console to the gamecube or even N64, which both suffered in sales. The N64 finished well behind the playstation, and the gamecube was blown away by the PS2, and fell to third. With the Wii's sales trends, it'll most likely be the top selling console, and game developers will take notice of that and build games for it.
Last, Nintendo is personally taking the initiative to go after mature games. Nintendo has aggresively pursued rockstar, and other game developers to release mature games, they've even tried getting the grand theft auto series. Nintendo is doing all it can to get mature games, and with console sales as they are, developers can't ignore this system.