The match ratings make very little sense, even if you break it down per position.
When a forward misses a chance, his match rating goes up.
When a midfielder dribbles the ball for several minutes only to end up giving away possession, his match rating goes up, sometimes by 2 or 3 points. (The most significant examples of this are in U21 matches, but I digress.)
When a defender (or any player) commits a foul in a position for a dangerous free kick, but doesn't receive a card, their match rating is unaffected.
When a team concedes via a penalty, the match rating of every defensive player decreases, instead of just the player who committed the foul. In addition, the goalkeeper's rating should not be affected much if he doesn't manage to save the penalty. Conversely, missing a penalty should result in the penalty taker's match rating decreasing by at least 1 or 2 points.
As it is now, the match rating is meaningless, even relative to other players in the same position.