To be honest, I don't know if I would have said that. I think that employees in "creative" positions (e.g., you're not serving customers at a bar and need to keep the shop open and working) are paid based on the output they produce. Whether that output is produced in 2, 6 or 8 hours is not really their problem. Looking at it this way, they would have happily paid you 100% of your salary for the same output you're now giving them with a 20% discount.
I work in academia and this was a tenure track position - these are quite rare and I have the feeling that only those will get these positions that can work 100% in 50% of time anyway (which accounts to 200% of work in a regular 40-hour job). I just wanted to make absolutely sure that I will have a limit of 6 hours a day and can take care of my body afterwards. Sitting 8 hours is just not doable anymore at close to 40, at least not for me.
