Human beings are only capable of sustained attention for limited periods of time, plus they have biological needs and must navigate a physical world.
Now, if you're just talking about time on the clock, then sure- 168 hours is the limit per week. But we're talking about people doing productive, mentally demanding work. 80 hours might not be possible.
It's definitely possible. Just because we don't want to do it (I don't either!) or that it has negative long-term consequences doesn't mean it's not possible.
I'm aware of the legal limit and every single resident I've met has broken it at least once (really at least a couple times every quarter). The "good" programs will at least not require their residents to lie about it.
It is real hands-on-work. There simply aren't enough doctors who are willing to work in a small town, even though they would get paid a lot more. From what I understand, anesthesiology (and surgery) is mostly autopilot work, so there isn't that much creativity, but it still requires thinking. Usually people respond to drugs the way you expect them to, but you need to be able to handle situations where things go catastrophically wrong.
Emergency Medicine and Critical Care manage to do handoffs well, as well as nursing. I strongly disbelieve that surgeons are uniquely incapable of doing handoffs.