What drives a fanboy?

I never understood what makes a "fanboy." I had only Nintendo consoles until Christmas of 2008, but I would be one of the first people to critisize the Wii and point out that it was very far from perfect.  What brings this up is something I saw just now on IGN. They had the "Console Showdown 2010," which first of all I think is just in itself troll and fanboy bait. Sure enough, at the time of writing this the article has been up for 90 minutes and there are 802 comments. I'm not going to go through and read them, but I bet the majority of them are complaining about the 360 being named best console of 2010, or gloating.
 
So what makes a fanboy a fanboy? Is it defending your purchase? Maybe, but I assume many of the people who flame others for liking a certain console are at an age where their parents are still buying them the consoles and games. Are there any reformed (or current) fanboys out there that have reasons for it? I feel like you don't see this as much in other mediums, sure there are people out there saying "my car is the best all other cars suck Fords are the best!111!!," but you hardly see that in comparison to games. Maybe those people just don't know how to use the internet.