Well, it's like the console wars. People tend to flock towards reviewers and critics they tend to agree with. IGN has become a big deal because a LOT of people like it, and agree with it's point of view, making it one of the more influential sources when it comes to gaming and geek culture. As a result those who don't agree with it, tend to be increasingly resentful because of all the people that do, and the weight it pulls.
As odd as it sounds I think IGN winds up exercising a little more freedom of opinion than other similar sites, even if it's still very topheavy. While IGN is manipulated by the industry due to IGN's dependance on it, the sheer popularity of IGN and size of it's organization gives it a little counter-pull, as does it branching out into more things than just games. As a result while IGN can't tank a popular/expensive AAA title from a big publisher, it can be less than glowing about it in a way that other similar organizations can't. Thus series fanboys get upset when they become used to "everyone" loving their mania of choice and see a major organization saying otherwise even if they aren't exactly negative. The same applies to their high ratings of products that otherwise wind up getting panned, which usually amounts to the amount of advertising dollars behind them (ie the less money behind a game, the more honest you can be), in cases like that it's usually IGN's reviewers simply liking something that other sources didn't, and that is why we have differant reviewers and critics, with differant points of view.
I'm not a huge IGN fan, this is just how I see things.