I think fanboyism is part of human nature. It...
1) Gives a sense of belonging to a community
2) Makes us feel that we are defending our community, thus making ourselves feel more needed
3) Allows us to hassle members of other communities, potentially in the hope of extending the community through this hassle
4) Allows us to vent our agression on others without offending members of our community
When you think about it, these elements are also prevailent in gang culture. When you think about it, it's probably better that these nerds are arguing over technology that shooting each other up (although seeing as nerds are more likely to shoot each other up through Counterstrike or Halo than through real life, it would mean for a hell of a lot more n00bish clans.)