As a fellow aficionado of the Tube, I want to comment. A century ago or so in America (and as far back to the Ancient Greeks), people would go to the theater for entertainment. They would watch live performers in front of them, singing, dancing, acting. That's what they would do on, say, a Friday night (of course, not until the weekends were invented as a result of labor laws).
What did TV bring? It brought shows into our homes, in our own privacy, we could watch. TV sets became more and more available and we got used to it as entertainment within the home.
Anyway to get back to your question, I think that the studios used to take more pride in showing entertainment close to what you would see in a playhouse. The actors memorized all their lines for the show and rehearsed and rehearsed because they knew they would be performing live, in front of people. Nowadays however, the TV producers have caught on to what the filmmakers were doing to be successful. They were editing seperately filmed clips together for form an entire, coherent movie. TV shows, with the exception of, say, Seinfeld, seem to be much more interested in making serial mini-movies for the TV, e.g., West Wing, ER. Despite this, maybe the marketing people at the networks have realized that there needs to still be some sort of entertainment that provides a sense of real-time theater. A good example of this is Saturday Night Live, and may be a good reason why the show has been so successful. That's my guess.
Did you know that the TV was invented by a person who thought that his invention might be useful by displaying cycled photographic images of wanted criminals, to facilitate their capture? In actuality, we all know that enterprising American companies gave the TV it's real original purpose: to display cycled images of their products to boost sales (advertising). How could they manage to get people to keep staring at these advertising boxes? By cleverly placing entertaining programs in between the commercials. Clever, huh?