A number of reasons.
-Fanboys that just can't conceive that "game b" is better than the game they bought or from the company they support (ie: people that think inFamous SS is better than SS Overdrive)
-People that let others think for them (ie: people that believe a 91 on Metacritic destroys a 90 on Metacritic)
-People that have gamed enough to be informed and know what they like (ie: Me!)








