it's all a bit funny
You always hear the British complain that the Americans simply don't understand irony. My question is, does the average person even understand the definition of irony? (Alanis Morrisette ruined it for impressionable youths everywhere by claiming that a series of bummers was ironic.) Furthermore, is it accurate to define the majority British comedy and the British sense of humour as being ironic? I think it's more a matter of degrees of subtlety. For example, let's imagine that you have just insulted your close friend with a witty barb. If your close friend is British, he will react with a statement such as, "Hmmm. Yes. Quite." If your close friend is American, he will react with a statement such as, "Oh yeah right, like you're EINSTEIN!"
If the Americans don't do irony, the British don't do blatant sarcasm - or they don't react to it very well, in my experience. British humour is more subtle, if you discount things like Carry On films, Benny Hill, and Reeves and Mortimer, of course. I think there is a common ground, though - both sides find humour in the very silly. Most of Monty Python's humour was very silly, and some of the best sketches on Saturday Night Live (back in the old days when it was still funny - those of you under 30 may not remember that era) was soaked in silliness. There is an international appreciation of the comedy of the absurd, which is why something like Austin Powers makes people giggle on both sides of the pond (and may I just mention that he is portrayed by a Canadian? I thank you).
Americans will understand the humour of The Office - they created Larry Saunders, you know. Okay, so someone will need to explain why Slough is funny, but everyone can appreciate a stapler suspended in gelatin.