Why is the Britcom season so short?

The title says it. Why is it so few episodes are made in a season or series in Britain? I’ve been watching Coupling on PBS and it’s just about to the end of the available episodes. I think there were 22 and that’s three seasons worth. I saw on the web that season 4 is in production or will be soon, but why so few episodes at one time? What are the contracts like for the cast?

From snpp.com:

I’m a big fan of The Good Life. It ran four series of seven eps each plus two specials.

On the DVD’s is an interview with the show’s creator and writer. He said there were only so many shows he could write about the show’s primary plot (40-yr-old man and his wife quit the rat race to become “self-sufficient”) without duplicating previous stories.

Think of most any long-running US sitcoms that re-hash the same story 2,3, or more times.

You have to remember that historically (certainly when you’re considering oldies like The Good Life) the British TV industry operated in a much less commercial, more “public service” environment than US TV, the idea being that the unfettered market did not provide the public with the best possible TV. On the one hand, this freed it, to some extent, from vulgar commercial responsibilities such as making TV programmes that people actually wanted to watch (or, to put it another way, allowed it to take creative risks, and to let programmes die when their writers ran out of ideas). On the other hand it limited its income, which was already much smaller than that of the US industry, which meant that it couldn’t have afforded to hire enough writers to make sitcoms that were still funny after 100 episodes if it had wanted to.
But should a sitcom run for 100 episodes? I’m glad Fawlty Towers didn’t, I’m glad Frasier did. It has to be said that the American system does seem to have produced better shows than ours in recent years.