Ehhhh... I'd argue that if you are working 80 hours, they likely aren't all productive hours due to fatigue, unhappiness, and loss of focus. Most of the time when I see people who work a lot of hours I generally think they aren't being very efficient and are probably wasting a lot of time.
A lot of my team mates that seem to be in the office after hours tend to spend most of the day socializing and bullshitting. No surprise they "stay late" to get things done.
This is surely an interesting topic to me. In one of my previous jobs, we were required to work at least 45 hours a week. Actually more than one, but the Navy doesn't count.
The hours weren't necessarily set, and it wasn't really written down in company policy (because that's illegal for exempt employees), but I did find it on a power point file. As my boss put it: "Studies show that people aren't productive 100% of the time. However, if you are required to work an extra 5 hours a week, an extra hour a day, we KNOW we are getting a good solid hour there, because why else would you be working late if you aren't working??" Ummm...many bosses at the job were like that and...honestly during my first review he dinged me because our VP and I would chat for the 5 minutes before our meeting started once a week. "If you want to talk about personal stuff with people, you can do it for a few minutes first thing in the morning, or right before you leave. But it's not good to do it in the middle of the day because it's distracting you from your work." I shit you not. Rather than argue (like wrestling with a pig), I just said "um, okay".
I don't think he's that bad anymore, but I really don't know for sure.
In any event, I found efficiency to decline with increasing hours. There was a period of time when I was working 32 hours a week, and they were solid hours. I worked with one or two men who worked 50-60 hours a week ("worked" is a strong word), and they liked to TALK. I would cut them off. One of them made a comment loudly every Friday when I left at 4:30 to pick up my kids (but only if the boss were around), "Must be nice to leave at 4:30". I said "Ed, it's not my fault that I get more done in 32 hours than you get done in 50."
Other studies have shown that working late is what helps get you promotions. "Face time". It doesn't matter if you actually get more done, the boss sees you working late. The boss doesn't see me come in at 7:30 am. It depends on the boss, obviously, but one of my previous bosses worked exactly this way - and I opted out of playing that game.