My memory could be faulty, but in British English, wouldn't "two-thousand AND ten" be two-thousand and ten one-hundreths? (2000.10 or 2000,10 depending on where you live) I thought I heard that in elementary school.
Anyway, the argument of "that's what they said back in the day" is not effective, as language is dynamic, and changes over time. The word "sheriff" was originally a contraction of "shire reeve", but if you go around using the latter term, it is unlikely you will find someone who understands you. (Source: Wikipedia, so grain of salt and such)
I could go into the psychological function of language, but the short story is that when we reach the day when I can go outside, say to someone "kthxbai" (or however that sounds when spoken), and have them understand without explanation, then that phrase will successfully be integrated into the English language. Yes, that is unfortunate. Believe me, I know.
Regarding the issue at hand, all that means is whatever we choose to say is right! There, you're free! You don't have to argue about it anymore!