Refs decide a lot of things, bit like the Fazio call today. Roma deserved to get through but also by the letter of the law should be out. Some teams do get more decisions, it's hard to call and to take, but having a passionate home crowd helps over a period of time.
That said, the deflection off Milner was not an easy thing to see, and I don't think City have the concentration in defence to keep a clean sheet anyway.