I'd argue that 100% of all humans use the decimal system, most of the time. Maybe 1 to 5% of all humans use another system some of the time.

Anyway, there are 10 types of people, those who understand binary and those who don't.

Because, as xkcd 169 says, communicating badly and then actung smug when you're misunderstood is not cleverness. "Orders of magnitude" refers to a decimal system in the vast majority of uses (I must admit I have no concrete data on this, but I can find plenty of references to it being base-10 and only a suggestion that it could be sometihng else).

Unless you've explicitly stated that you mean something else, people have no reason to think that you mean something else.