it has been observed here by members of the UKind that USns just don't get irony. this morning I found, on another word forum, a post by "arnie" from London that I think explains the whole problem rather well:

Irony is a form of expression in which an intended meaning is the opposite of the literal meaning of the words used. So if I were to yell "Nice driving!" at another driver who had just forced me to brake sharply, I'd be using irony.

Sarcasm is intended to wound or hurt another; it is intended to make its victim the butt of contempt or ridicule. If I were to nominate GW Bush for the Nobel Peace Prize I'd be using sarcasm.

There is often a fine line between irony and sarcasm: the difference is that sarcasm is used with intent to wound.

The English use irony very often when making humorous remarks, and this sometimes causes friction in their dealings with Americans, who mistake the irony for sarcasm.