"There's another way to understand what has happened to American comedy in recent years: it has become more British. The hallmark of a British sitcom is a quasi-unbearable protagonist who is an Everyman, only insofar as every man can laugh at him. The unrepentant snob Basil Fawlty, the beastly glamour-pusses Edina and Patsy, the fatuous narcissist Alan Partridge, and the thirsty buffoon David Brent: these classic British characters are all flawed in the unapologetic manner of contemporary edgy American comedies.
UK sitcoms tend to be darker than American ones, encouraged by a powerful public broadcasting system whose aim is to serve the varying tastes of taxpayers, not the upbeat preferences of advertisers, and by a national psyche fixated on the immutability of the class system, not on a dream of self-improvement. Americans believe that things will get better. Brits laugh at how things stay the same. To become a hit in the United States, The Office not only had to transform the tragic, grating boss into a less tragic, less grating, more well-meaning boss; it had to cast off the message, central to the British original, that work is where you go to waste your life."
Writing about Sharon Horgan's sitcoms Pulling, Catastrophe and Divorce, Willa Paskin of the New Yorker perceptively puts her finger on the fundamental differences (historically speaking) between British and American comedies. She suggests that Divorce, which has been made for HBO, as an illustration of her argument that American comedy "has become more British".
It's this transformation, I think, that has led to me warming far more to US sitcoms than I ever used to; Curb Your Enthusiasm, 30 Rock and Arrested Development both appeal to my sense of humour in a way that older series simply didn't.
(Thanks to Damian for the link.)