I'm pretty sure the "review rules" are just certain restrictions that the company would rather not be mentioned or centered on in the review. However even if they don't mention it; that doesn't mean they are bound to not lower or higher the score due to said aspect. As for MGS4 if reviewers mentioned it a lot of people might wanna say OMG NO GAMEPLAY AND ALL MOVIES... which is false in at least MGS4's case. I personally don't like the idea of rules but not much anyone can do about it because reviewing MGS4 or any other blockbuster early is bound to get you attention and for websites like IGN this = money.
Hopefully future games won't follow this, because I can see this slowly and slowly becoming worse and worse till the amount of censorship would be obvious even if they reviews didn't announce they were censored partially before they started making comments on the game.
