People would avoid mandatory exercises.. It would probably INCREASE absenteeism. And on top of that.. there are other issues to consider. For example, I have Spina Bifida, are you going to expect me to jump out of my chair and jazzersize? or wave my arms around when my back is in excruciating pain?
I am all for the 20 hour work week. This represents a problem though.. I know I spend a lot more money on my days off than I do working, sure I would manage it if I had more days off, but not everyone has money managing skills... Think about it, I doubt this is just me, but you do more things on your days off, and those things cost money...
Also, what about 24/7 operations? Doctors, Kwik-e-Marts, etc.. If you have a 20 hour work week, you have to hire twice as many people to cover all the hours. Are you going to cut wages in half?
Sure it works in an office setting, where you have specific tasks that need to be completed, but how do you man a desk that always has to have someone behind it?