I think the problem is that Xbox 360 and PS3 have far more hardcore games to choose from. Wii does have a lot of great games and more than one person who has a job or school or something else in their life could realistically play. It would be like walking into a Blockbuster, you see thousands of movies there but you're only going to rent a couple anyway but you have so much to choose from. With the Wii, it can be like going into a small family video store that has the big titles and all the Disney and kid movies but not many of the smaller or "hardcore" ones that are also great. So sometimes Wii owners can look to Blockbuster and see stuff they want but can't get.
It could be some sort of jealousy when Wii owners see games they want not coming to their system but instead one of the other two. I'm a Wii owner but know that eventually I will get one of the other systems because there are some other games that I want but the Wii won't get.
I'll come up with something better eventually...
