I don't think the fact that there are multiple words that represent the same thing means that one is ambiguous. A "billion" is always 10^9, so it's not ambiguous, no?
It looks like the Long scale is falling into disuse in English speaking contexts from that article. I don't ever think I've ever seen the word "billion" in English refer to 1e+12 .
No, it's the other way around. A billion means one thing in english speaking countries and another in most of the rest of the world. For a frenchman, it's indeed ambiguous -- there, a billion (english) would be a milliard (french), whereas a billion (french) would be a trillion in english. I imagine that is the reason why it's not seen as an abbreviation, in contexts where you want to be accurate.
