Maybe the whole quality of television thing I brought up in my Dr. Who post has to do with the sheer number of episodes a year they have to produce. There's usually around 24 episodes per year of a show, minimum. Can you produce that much stuff and not have it come out stupid?
Of course, there are great American shows that don't treat you like a moron...The Shield, Dexter, The Sopranos, and so forth. You only really get them on pay channels or cable. It's the networks that have to do wall-to-wall programming and, as a result, get so many episodes of each show that the quality has to suffer.
Once again, everything is the fault of the big businesses...and let me tell you, that makes me feel much better.