I have known a number of Americans with absolutely delicious senses of irony. I must say that part of the impact may have been due precisely to my prejudice - that I didn't expect Americans to be able to get it, or prepetrate it. But it is absolutely brilliant when they do. I have long since given up the notion that Americans don't 'do' irony. It is simply that perhaps it is so subtle that even we Brits don't get it!