Probably 10-20% of the people on the dev team just loved it. They couldn't get enough. That includes engineers and artists. They could work from 9am to 11pm for months.
But then management expects 100% of people to be like that. And there's peer pressure not to let down your coworkers. But in reality some people just have more stamina, and can get more done with the incremental hour, while for others it was just clocking time and being a zombie.
I definitely couldn't get much more done in all those late nights, although it in part it has to do with the fact that there was some sort of "schedule". If you know that you can take a day or 2 off whenever you want, you're likely to have more stamina for a 16 hour bender.
Anyway, there is so much human variation in other things; it doesn't surprise me at all that it's true for how many hours you can productively work in a day. I would bet startup founders need that stamina, although I'm sure there are many more components to success.