dave weil said:

I'm pretty convinced that it's mostly a storage issue. NBC seems to
use a particularly bad compression scheme. You seem to support Mr.
Pierce's contention that there's a bandwidth issue as well in terms of
the actual broadcast. Now this is just speculation on my part, because
I don't have cable any more and I can't watch NBC to see if cable
treats it any better (maybe I'll just ask a cable-equipped friend to
switch to NBC during network prime time the next time I'm over).

The cause of your compression might not be NBC per se. On my cable feed,
the NBC station is about the same as CBS. ABC and HBO might be a hair
better, but it's not an obvious difference. However, I get more
artifacts and freeze-ups on ABC shows than any other network. Also,
sometimes on NBC shows, the widescreen HD version disappears for part of
the show, and all you get is the standard 4x3 version. Then it'll
randomly switch back to the HD version. Do you have that problem with
Dish? I'm sure it emanates from the source, i.e. the local broadcast
station.