Code switching between registers is a fact of life in America. Nobody speaks corporate natively, and it's more extreme if you grow up or live in an ethnic minority enclave.

What Americans tend to not "get" is how dry British humor can be. It's less about not getting sarcasm and more just not finding it as funny. Personally, I blame the number of ads that interrupt our TV shows back when people watched broadcast and cable TV. There really wasn't enough time to build up and the ads are too loud and shouty in comparison.