My reaction is like dvhervey’s. I am not offended, I just don’t know what to make of it.
I am assuming you are asking if we are offended from the US point of view that someone is making jokes about a tragedy? Apart from the fact that I’m not American (and was not half as distressed about seeing the twin towers go down as most people here), I generally believe that humour does have a way of exorcising tragedy. I remember how much we joked and laughed at my aunt’s funeral. And that includes my father (her brother) and her two sons. The actual events may be distressing, even tragic, but humour should not be constrained as a result. It is the means of getting you through to the other side.
I remember once I told a joke about drugs and someone said “you shouldn’t joke about that, taking drugs is a serious issue and people who take them suffer and even die as a result”. And I thought of all jokes we’ve ever said: isn’t it serious when “An Englishman, a Frenchman and a German fall in the jungle with an aeroplane…”? Or when “a blonde, a brunette and Santa Claus fall off the Empire State Building…”? Or basically most situations like that?
So yes, humour can often be wry. It doesn’t offend me at all. I just didn’t get the joke much in this case.