Bad refs aren't a new invention, they have always been there. The thing is, as United, Liverpool and Arsenal have proven over the years if you have more possession of the ball than the opposition you are much more likely to get decisions in your favour.
They get more penalties because they are in the opponents area more often.
Some refs are better than others but it's really up to City to negate the effect a poor referee can have on the game by playing well in games like this.
I don't think it's so much the refereeing decisions that rankle it's more the lack of consistency of decision making and the really poor leadership from the F.A?