The reality favors Nintendo argument seems to have become the battlecry of late, but it's a flawed one. Unless we count portables (which nobody's done for the past decade), the market overwhelmingly remains Sony's, despite Wii's leadership of about a million per territory, and Microsoft is still the next gen market leader. My personal advice would be to accept it rather than attempt to come up with a weak rationalization. Any attempt to change it would require posters actually interested in Sony/Microsoft systems. As the only person arguing in Sony's favor in a lot of threads, I can tell you that's something that there isn't any of, and it's not something that I can see as being easily changed.
Calling Nintendo kiddy should be fair game (and not just because it's true). However, I do believe that people shouldn't attack each other. I'll get sarcastic with people because I always am, but I won't start with namecalling or anything along those lines. I don't believe anyone's called me names, but I've had my share of people telling me things like I don't think before I post (for no other reason than that I disagree with them). I just shrug it off as ignorance, but some people will take it as an invitation to lash out.
So anyway, to answer the original question:
Stat bias: slightly, but not enough to remove their usefulness (the bigger problem is the lack of reliability of stats for the US and moreso others).
Forum bias: I'd say it's about 5:1 in favor of Nintendo, and that may be conservative. It's pretty clear ioi favors Nintendo as well, which could maybe be made a bit less blatant, but I don't think it really matters much one way or the other since I don't believe any administrator should either a) temper his bias or b) determines the overall tone of the forums once they become large enough.