Neat! I'll have to look into the history of that more sometime. I wonder if it's another thing (like the Mr./Mr discussion above) where UK and US usage used to be more similar, and then diverged, and as Americans we assume that the current British usage must of course be the original one, and our usage the one that diverged, when often it's the other way around! (As with got/gotten. And oh, probably lots of other things I can't think of right now!)