The site itself is absolutely not biased.
The community of course is mostly pro-nintendo, but this has several reasons I think.
First, as some already mentioned, the winner usually gets the most support and at the moment it looks like nintendo is the winner. Second, and this one is probably more important, most users with a lot of posts are pro nintendo. I can only think of mrstickball, shane, diomedes and kber81 not to be pro nintendo and having a lot of posts. But, and maybe you don't agree with that, but in my eyes the most respected people with the most resonable posts are pro nintendo. I'm thinking about Erik Aston, Alacrist, HappySquirrel and Sieanr for example. On the other hand, the four pro sony or pro microsoft posters I mentioned before are writing much more aggressive in my opinion, and this gives you the feeling that the anti nintendo guys always have to defend themselves because the forum is biased.
These are just my impressions, though.