My impression is quality has actually gone down hill over last couple years. A few years ago the difference between my OTA locals and Dish Locals was very small and hard to notice. It is very obvious to me now.
Another reason for quality differences from state to state, is sub channels. Each sub channel chips away at the bandwidth of that assigned frequency. I don't have the exact number's so I will use made up one's. If ABC gets 100MB's and they have two channels 12-1 and 12-2. Now you are at 50 and 50. They can assign say 75 and 25 giving the most watched the most goodness. That's there call. But I think you get the point. Years ago there were no sub channels so what you saw was the best it had. Hope this helps. If you want real numbers I can get them if you want. Peace