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CerebralTiger
The scores for all games should be from the same platform for fair comparison. Reviewers rate games according to the platform. When they praise graphics of a game on PS3, they are comparing it to graphics of other games on PS3 and don't take graphics of PC games into consideration. The game might get high score due to that on PS3 but reviewers reviewing the game on PC might deduct score due to graphics being lesser than other PC games.
I know there might not be any difference in scores from same publication/website. But there are many reviewers who talk exclusively about one specific platform. And amongst them Playstation or Xbox exclusive reviewers are likely to rate games on their platform a bit higher than PC specific reviewers. Playstation Official Magazine might rate a game highly because it's the best FPS on the platform while PC Gamers might score it lower as it doesn't do anything new compared to games already available on PC.
However, if you feel that Killzone Shadowfall is going to need 02 point advantage to be able to compete favorably against Battlefield 4 then sure, do whatever you feel is necessary