I don't think those are the right reasons...
I had a longer write up, but in essence, it's about age. How old is the average person posting on message boards/forums? Lets say, 16-25. That's a nice meaty range.
Lets say you started playing games when you were 5. If you're 16 when did you start playing games? In about 2002 right? So what did you start playing on? a PS2. If you started playing when you were 5 and you're 18 now, then you started playing around 2000 most likely on a PS1 or two. If you're 18-23 you probably started gaming on a PS1. Any older than that, and maybe you started on a Super Nintendo.
When you start something at such a young age, you develop a fondness for it. It's not just a game machine, it was part of your childhood. Many of your most precious memories are tied up with that device. It helps develop fandom that is a bit more extreme than typical.
Microsoft has only been in the gaming industry for 13 years or so, but only as a relevant entity for about 8. So, fewer gamers have really grown up on the 360. Nintendo has been around for longer, but from the mid 90s to the DS/Wii era, they were getting trounced by Sony.
There are other factors but that, in a nutshell, is why I think there are more Sony fans on the internet. It's a matter of timing mostly. It will be interesting what happens when the Wii/DS kids grow up.







