a better question is:
Why some sony fans are always angry with wii?
This is an easy one which includes more than just Sony fans. Wii success can mean in some cases (not all) more "dumb" down games. For example; There is no doubt Wii success had an huge impact of how the game Spores finally turned out. Spores was nothing like what the game start out as. Some neat ideas got dump just to make the game more accessable.