I remember reading a bit through the Plat Difficulty thread for LA Noire on PS3trophies.org, and a lot of people have said that they don't believe the game is as difficult as people are voting. A few trophies are tedious, but they believe that there are a lot of people just screwing around and voting the max for the game (there was something like 10-15 votes for a difficulty of 10 within the first 2-3 days). I think there should be three factors for the rating of a game on here: the difficulty of the game, the length of the game, and the amount of information readily available to help with the game. The last one involves the amount of trophy guides and info that comes out that can make a game, like LA Noire, become really easy. Obviously, this will affect the more obscure games, but over time they even get some very good and comprehensive guides.
Games that have a very long platinum time (WKC, Mortal Kombat and Star Ocean 4 are three games that may not be the most difficult, but take a long time) should definitely be a factor. All three of those games probably take upward of 400-500 hours, which seriously cuts into playing other games and the like.
EDIT - Some people say they don't use guides for the first playthrough or at all, but it should still be a factor in the ratings.
