Well, as I said, the company would monitor the pilots and ensure that they were not flying fatigued.
Anyway, my airline pays overtime after we hit x hours in a one year period so rostering is put under pressure to ensure we don't exceed those hours unless absolutely necessary. Recruitment and manpower also ensure that we are staffed to ensure that overtime is not common.
I also agree it's not necessarily hours much you fly but also the manner in which they schedule you. Constant changes between day and night flights is a killer. Short haul pilots need a routine. X days flying followed by X off, something that can be relied on.