I think that estimate is about correct. I actually thought about this for a while, and I think that between 750 & 800, each 10 points drops off about 1/2 or more of the people from each level.
We know that 750 is 99% which out of 200,000 that take the test each year is about 2000 people. So, tell me what you think of the following estimates:
750 ~ 2000 people per year
760 ~ 1000
770 ~ 400-500
780 ~ 175-200
790 ~ 50-60
800 ~ 10-20
On the various boards, I have seen a number of 750 & 760, but very very few 780+.