I used to work 60-80 hours a week in the summers and 60+ between a full credit load and a couple of part time jobs. I went to bed twice a day for a couple of years because I was working swing shift and going to school.

I now have a 9-5 office job. I am apparently capable of working at least twice as many hours but I choose not to because I don't have to.

There are already people making twice as much (and more) than I do in as much or less time.

I don't think a 20 hour week for knowledge workers would have the effect you claim.