My guess is that HD, needing a larger bandwith, would display the compression more so, than SD, and, SD, being a lower resolution, would mask the compression better. I did a few installations in my friends houses, who use cable, and I was able to reduce the artifacts with better cables. I haven't played with HDMI on thier (cable) sets, but when I replaced the poor component cables that come with cable boxes, with top of the line Monster Component Cable the difference in picture was staggering. (a neighbor of a freind of mine went out and bought the same TV when they saw her picture and was very dissapointed when it didn't lok as good; the difference was, indeed, the cable.
When I had cable, I fought with my cable company to lay a new cable direct from junction to my home, instead of splitting it among the other residents in my development, and the picture was much, much better (almost as good as my sat picture-almost.
When I had cable, I fought with my cable company to lay a new cable direct from junction to my home, instead of splitting it among the other residents in my development, and the picture was much, much better (almost as good as my sat picture-almost.