I have it on good sources that they don't get bribed, at least not directly. What does happen is that publishers that would have sent you an advance review copy of their latest game or invite you to some showoff may not be so willing if your publication has reviewed some game in a way they deemed unfair. So there's some conflict of interest there, since getting review copies and getting into the latest demo showoff will give your publication more readers...
AFAIK that's pretty much standard operating procedure in the game "journalism" industry, since getting early review code is one of those things that's almost guaranteed to bring in more page hits/ad revenue. It's been standard operating procedure for games reviewers for a long time, actually.
... personally I would much rather have reviwers who know
Yes, in an ideal world, there should be an "FPS guy" handing shooters, a "strategy guy" handing TBS/RTS games, an "RPG guy" for role playing games, and so-on. But sadly, to maximize profits they often stick to having as slim a review staff as possible. Hence you get situations where a great adventure game may get slammed by a writer just because it didn't conform to what his opinion was of an interesting game.