It's a sad truth; I've seen it happen.
If you want to be competitive when writing game reviews and previews, you have to show exclusive early looks at content, because that will bring in readers.
If you want exclusive early looks at content, you must appease the content creators, which means giving them good reviews.
It's a vicious cycle; give someone a bad review, lose your early preview privileges, go out of business as your competitors gobble up your reader share.
Now you could always run, say, a website that only posts reviews, and posts honest reviews. You would never get preview content, you would have to purchase your games like everyone else, and you'd probably get some hate mail and even a C&D or two, but you would be free to write unbiased, unvarnished reviews. One would think that a consistently good review writer could write a blog and get a pretty good rep and readership like this, but a consistently good writer like that would be the kind of guy you'd snap up, put on a payroll and then tell that he can't write negative press.