Sound a bit inconsistent - why weren't 10 - 20 also changed? Would have been great to have a language that's consistent all the way through as far as counting is concerned :)
It's after this that you get "twenty-one, twenty-two, ... " and up to "ninety-nine" - which can also be pronounced "one-and-twenty, two-and-twenty, ..." up to "nine-and-ninety".