For me, it has to do with the lack of variety in the weapons. I mean, developers can't rewrite history, so every WWII game has the same set of guns to choose from. It gets boring.
My End of 2008 Hardware Predictions (console only):
Wii : 50 million
360: 28 million
PS3: 24 million
These predictions were made on January 3rd and won't be revised