The rest of the world is technically wrong. Mathematics is a singular noun, due to the way -ics is handled by the original latin/greek. On the other hand, -th indicates a singular verb as well, so when you throw that s on the end of it, you're making it (incorrectly) plural.
However, I said it was technically wrong for a reason. Language is dictated by usage, not semantics. It's the reason why the word "ain't" is in the dictionary today. So even though maths may not be technically correct, the widespread usage of the word dictates that it is.