Look at the history in the PL mate. The amount of decisions they get at crucial times is a joke (and I mean CRUCIAL decisions that change games) Man Utd fans sometimes moan that bad decisions go against them but it's usually when they are already 3-0 thanks to ref and makes no difference to the final result. It's not so much the quantity it's the timing, it's the game changers.
Forget history, lets look at April 2012. Cast iron penalty refused in Wigan game. Score at the time 1-0 to Wigan. Final score 1-0. Man Utd DO get their fair share of poor decisions.