IMO the "milliard" convention is absolute rubbish, because it effectively breaks the decimal system and I'm glad it's in decline in the English speaking world. I wish the same were true for its use in other languages as well.
OK, we're drifting off-topic now, but I just wanted to say that I completely disagree. There's nothing "decimal" about million->billion->trillion going up in factors of a thousand rather than of a million, it's completely arbitrary. And etymologically, a billion being a million million makes sense: the "bi-" means "two", and it has twice as many zeros; similarly, a European trillion has three times as many zeros as a million, hence "tri-". What are there three of in an American trillion?
Multiples of a thousand. As you say, both conventions are mathematically arbitrary.
I would, however, like to point out that this "etymology" business is nonsensse. The word "billion" (and the convention thereof) comes to us [English speakers] from French, whose system we [Americans] continue to use despite the fact that France itself switched systems fairly recently in history (and for quite sensible reasons). In short, we have kept the original definition, while Europe has standardized on another. I can't say that I have any problem whatever with that.
I'd also like to note that virtually all Americans are completely oblivious to the difference, and to the best of whose knowledge a milliard is some kind of waterfowl. I was no exception, given the fact that my foreign associations have always comprised mostly scientists and academics, who by and large agree with my personal preference: to have a name for each additional placeholder.
It's a moot point, because the American version seems to have become the accepted standard in the English-speaking world (better than just remaining ambiguous for eternity, I suppose), but the old way is far more logical. [I've actually heard it suggested that the change was so that people could call themselves "billionaires", but I'm not sure how much truth there can be in that]
I was recently somewhat surprised to find that even BBC World Service broadcasts have adopted the "American" convention for numbers, albeit with an occasional parenthetical clarification. That said, a clear divide on the issue obviously remains, although in our particular case the intrinsic problems can be avoided by enumerating large sums.
(Of course, this brings up the issue of commas vs. spaces as placeholders, but that's another can of worms.)
-- Rowan Collins BSc [IMSoP]