I think you're trying to equate a 10 with perfect, which no game will ever be. Usually sites that review have guidelines that specify what the ratings mean. For example, a 10 to IGN is a masterpiece, which is:
"The pinnacle of gaming, a masterpiece may not be flawless, but it is so exceptional that it is hard to imagine a game being better. At the time of its release, this game is the not just the best the system can offer, but better than we could have expected. "







