You're comparing apples and oranges. I already stated for the record that DISH and DirecTV compress 12 signals onto one satellite transponder. A local HDTV station is going to have the luxury of allocating themselves the entire spectrum of one channel, or devote other parts of that same signal to things such as Weather+Plus (NBC weather product) for example.
You're explaining why the Dish and DirecTV pix are worse than off air images, but that doesn't mean it's an apples/oranges comparison. It's a comparison of video images from different sources. It's all apples (or oranges.) Some apples are not as good as others.