exactly. Fawlty Towers wouldn't be half as good if it was 20 episodes or more. The characters are one dimensional and eventually they would grow annoying. But at it's two "series" length it works perfectly and is regarded as one of the best britcoms ever.
I remember John Cleese felt when the Python's wanted to do a 4th series of Monty Python he found them absurd and thought going into that length was far too long and insane.
