I think these numbers are way off. I read an article on lexicography years ago. The numbers in that article were:

Vocabulary of average high school student: 8,000

...of average college graduate: 12,000

...of average person with advanced degrees: 25,000

...of average lexicographer: 100,000


And the English language at the time was supposed to have included 600,000 words, but I've read since then that it had grown to 800,000 +

Again, I think these numbers are way off in the Newsweek report.

My two cents,
WW