Certainly there could be a source of bias in some of the reviews when the publisher is advertising on the review website. I think you guys are taking it a little far though - most of the reviews I read on metacritic I find to be quite fair.
Black Ops wasn't the best game of all time, but it wasn't reviewed as such either. IGN's review gives it one of the higher scores (85/100) but it clearly mentions the poor AI, linear gameplay and how the game plays part of the singleplayer for you. I would have probably given it about an 85 myself, and nobody is paying me.
The main difference between the critic reviews and the customer reviews when it comes to Black Ops is the discussion of bugs and glitches. The very first customer review as I type this states that "Black Ops is unplayable on a PC". I played it just fine on a PC and while I sympathize with posters who have had many troubles, there are also plenty of us who have had few. I don't know what the common denominator is but with the hodgepodge of computing hardware and drivers that people use, I tend to discount complaints about bugs heavily.
Also, look at how many of the user reviews are either 0 or 1 on metacritic. They need to employ a formula like IMDB does to eliminate the low and high scores from the hordes of internet monkeys who can only think in binary.