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Preserving the old big block here until someone manages to slim it down to the three big differences: Historical In Jokes, British Brevity, and lack of Pop Culture references.
With a single memorable exception, it can be hard for foreigners to get into. The Historical In Jokes alone are practically a Continuity Lock-Out: Brits have a lot more history than Americans, are much better educated in it - and dearly love making fun of it. Ninety percent of the humor in Blackadder is that it's basically Hercules The Legendary Journeys played for extremely morbid laughs, Rowan Atkinson is the British Seinfeld, and his spoken parts are every bit as steeped in British popular culture. Even the internationally loved Doctor Who suffers from this; when the Ninth Doctor insisted that "Lots of planets have a north", you weren't supposed to just snort— you were supposed to go into a Jim Carrey-quality diaphragm spasm, you heathens! Yet, despite all that: American sitcoms are also very typically... well, American. Many of them tend to rely heavily on pop culture references and celebrity guest appearances. Sitcom characters referencing or spoofing Hollywood films, American TV shows, comics, pop singers or even TV commercials are not uncommon. Even though a lot of these things also reach the other parts of the globe thanks to America's mass media imperialism, not all of this stuff is as well-known there as it is in the U.S.
One important facet of British TV that distinguishes it from American TV is that the number of different British TV program[me]s is higher than in America, simply because British TV programs are shorter and cheaper. The UK standard for the length of a TV "series" (equivalent to a "season" in the US) is anywhere from 6 to 8 episodes. By contrast, a successful US series will often have a single season of 20-30 episodes — with each episode a half-hour or an hour, this means that an American TV cast will, through the course of a single year, have to film as much footage as several feature films. One of the major reasons for this is the differing way in which they are written: US shows frequently have writing teams of 20-30 writers - one writer said sometimes you'd be happy if just one of your lines made it in. Conversely British shows (especially the ones that are called "classic") tend to be written by just one or two people, often long term collaborators such as Gaulton and Simpson. In a programme comparing the two (where the quote about getting one line in came from) the point was made that in many US sit-coms many of the lines could be said by anyone on the cast - they are far more generic.
Compounding this is the fact that successful US TV shows will run for many more total seasons than UK TV shows. UK production companies have a reputation for being a lot better about ending a show when it's over, and letting showrunners have freedom over that decision; US producers, by contrast, have a reputation for determinedly running successful franchises well into the ground until they let them go, which is usually the point when it becomes too unprofitable to keep running them. Thus, a UK program like Life on Mars can be a "major hit" and still end in two seasons, which is relatively unheard of in the US; on the other hand, the number of successful American TV programs that have run for longer than a decade, Jumping the Shark multiple times in the process, is too long to list. (Of course, the UK has its notable exceptions, like Doctor Who and Last of the Summer Wine — and the former had a long hiatus in the '90s and early '00s, while the continued survival of the latter is one of the things that still struggles to explain within the confines of a rational universe has finally ended.)
Three paragraphs in and America's probably been mentioned more than Brits. Feels condescending.
I removed as much of the irrelevant stuff as I could today, it was silly. Making a few international comparisons is worthwhile, but it didn't need to be explained in so much rambling depth. I don't know whether it was a Brit who wrote all that, but Americans know what to expect from American sitcoms, it doesn't belong in this article. Most of it looked like it had been copied from the British Brevity trope — mentioning Life on Mars and Doctor Who as "Britcoms"?! The article could mention that many Britcoms make it to TV in Australia, NZ, mainland Europe, etc. (But very few series come the other way — pity, as I've just seen this)
The section saying that you have to be a Brit to understand the comedy is all wrong. At least in New Zealand most people old enough to remember Britain doing anything other than depressing soaps understand most of the jokes.
I think the section is basically written from an American perspective. While it is true that some of the in-jokes may be wasted on foreign audiences, Scandinavians (myself included) also tend to appreciate British comedy, simply because the basic outlook on life is closer to ours than what is typically displayed in American comedy. There are still probably more American comedy shows on TV overall (at least in Norway), but they are generally treated as "light entertainment", are more likely to be shown during the daytime, and do not have the kind of die-hard fans that some British comedy shows do.
Shameless should be added in here, I believe. Even though its quality does run off in the later series, it's certainly not the usual American fare and has a strong sense of Britishness.
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