I agree w/ those stats. Most hygienists that I know work part time (no benefits) make around 50-60K/year. There are few who can make a bit more if they get 40% commission at a new office that is unsure if they can keep them busy every hour and don't want to pay high hourly rate if schedule is not fully booked. But this arrangement is always
temporary.
At my office all hygienist initially worked on commission but as soon as the patient flow became steady, they went to an hourly rate (which of course was lower). The couple hygienists that resisted, were let go. Although one recently came back b/c after going through that w/ couple other offices, she just wanted a steady job, with more than 1 day/wk.
My friend from dental school worked 7days/wk for first 3 YEARS after school, w/ long hours, but took home over $300,000/yr. So I guess if you don't mind putting in the time, more money is always possible.

(now he works 6days)