I imagine many people here will not be in the kind of job where you are actually paid by the hour and can easily adjust your income by adjusting the number of hours you work. I certainly haven't been in a job like that since graduating from university.
Even so, it seems unlikely that people will consistently be hired to work less than the ideal amount.
The amount of time you spend working tends to be about the same regardless of your job. It's not inherent in the job. It's the jobs being geared towards how much people will work.
Full essay: http://www.gwern.net/Melatonin