As for 30 Rock, it was important that the show didn't go on and on. Scrubs and Only Fools and Horses immediately spring to mind as programmes which should have stopped after fitting finales, but went on a little too long. Although a full-length final-series would have been nice, I'm sure that the final, hour-long episode will be a fitting one.
First, let me declare something: I'll almost always choose an American show over a British one and actively search the US network schedules and entertainment sites for something that tickles my fancy. But the lot of being a massive American television fan in the UK like myself is a strange one. If you don't want to risk tangling with the authorities by torrent-ing shows (and obviously I don't), you either have to cross your fingers a British channel buys it, or wait until something pops up on import DVD.