I have trouble buying into an official choosing not to call something he knows is a penalty. I do believe the Cowboys don't get the same calls other teams do, but I don't think it is because officials give the other teams preferential treatment.
I think the official just missed the hit. It happens.
Now, I do believe that when you get a reputation as a penalty-prone team, the officials are bound to watch you closer than they do teams that are less penalized. It makes it that much tougher to shake the reputation. (The best officials are those who go into games with a blank slate for each team, but I don't think there are many who do that.)