I would think that D* uses a spot-beam for your locals. As far as bandwidth there is a set amount per spot-beam. Depending on how many channels they put on that spot beam will affect quality. Having HD channels for ABC, CBS, FOX, NBC, and PBS, is pushing the envelope. If they put even more channels on the spot-beam, then poor quality is more frequently seen. Also using MPEG-4, they can get away with around 50% compression. When the TV stations are already pushing the envelope with narrow bandwidth, where the decompression can't recover all the data the receivers just can't replace it fast enough.
Another thing that the satellite companies do is have each channel on a sliding scale for bandwidth. If one station is using less, another station using more will benefit the bandwidth. If all the TV stations are all running at max., well you should get the picture.
If you compare KRCR, KCVU, and KIXE against KHSL and KNVN for OTA quality when there is fast motion, panning, and fast scene changes; KRCR, KCVU, and KIXE have better quality because they use 720p which just works better. If you look at a static picture, then KHSL and KNVN look better because of the higher resolution. It is too bad that the OTA channels are stuck in MPEG-2.
It may be worth while to complain to the TV stations about the quality for satellite reception as they do have a line of communication with D*.