Read Peopleware if you haven't already. It covers myths like the 60 hour work week and outlines how to make software projects productive and predictable.
Can have negative productivity. I am all in favor of keeping work loads light, but in real businesses edge cases come up.
We recently just got through a couple of really harrowing sprints because of such an edge case - a lot of hours were worked. Quality remained high. I personally am satisfied with what we delivered - while it could have been done better with more time, the tradeoffs were all understood and accepted.
The flip side of that is that this kind of thing happens to a given team here maybe once or twice a year. The rest of the time is sane, normal working hours and load. If it were like this a significant portion of the time, then you'd start seeing the kind of patterns you're describing.