This is just something that 3rd parties like to complain about. The truth is that GOOD 3rd party titles sold on the Wii. Both the RE sold very well (even considering the RE:UC is a rail shooter), GHIII has sold amazing and I'm sure the next well advertised or popular game comes out it will sell well.
Games like Manhunt, MoH, Scarface, Godfather, etc. are all bad games or a genre that where the horse was beat to death 5 years ago (not to mention MoH is one of the worse WWII FPS) or a uses a movies name, which always sells horrible.
Games that are gems like Zack and Wiki and No More Heroes (although NMH has yet to release outside of Japan so it could actually sell well) suffer from no funding for advertisements. I bet 90% of Wii owners would not have ever heard of either of these games, but I bet +60% of the general US populace knows that Halo 3 is out.
I just need to comment on this one, I would happily buy non-nintendo games if there was something there to actually buy (truthfully I own 5 games and only 2 of them are Nintendo titles, don't have the money to buy the other ones I want). Someone can quote me if they want, but I have to say that Nintendo is one of the greatest game development companies out there. When Nintendo releases a title, its always AAA. Basically if 3rd party companies would make games that actually compared to Nintendo's, they would sell just as well as Nintendo titles.I believe this is an issue that must be addressed by Nintendo itself because third-parties don't seem to have the balls to take a chance. The Big N, on the other hand, has all the necessary advantages. One, gamers like you are more likely to buy a Wii title published by Nintendo. You can deny it all you want, but you know it's true. Second, Nintendo has the resources to create a AAA adult-themed (and exclusive) Wii game -- or several of them, which would be preferable.