I don't happen to think that nurses are poorly paid anymore, but anyway.. Quattro - it's not just the hours is it, it's the nature of the work.
Some people do very physically and emotionally draining work that wouldn't be sustainable for more than a standard working week.
Some people work very intensively when they are at work, cramming in as much as they possibly can, working through lunch and not wasting time.
Other people, the ones with presentee tendencies, appear to work harder because they are in the office for longer. Look closer and you see they are not working efficiently and they are sticking their nose into things that are not their job.
These differences can be seen right across the board, so it's impossible to equate number of hours worked with how hard someone works.