I agree that it's surprising that (1) working long hours seems to have been found ineffective in academic studies and yet (2) businesses tend to want it. Aside from startups, I remark that the finance industry is notorious for extremely long working hours, and yet you'd have thought that (say) a hedge fund could benefit a lot from having its very expensive very smart people working more effectively if shorter hours would achieve that.

One possibility I've wondered about is that maybe it's about latency rather than bandwidth. In other words: If you're at work for shorter hours, then you may get more done but when someone else needs you -- especially if it might be someone else in a different timezone -- then they may have to wait a lot longer, and that may end up outweighing your greater individual productivity.

(I think I've seen something very like this offered as an explanation for investment banks' punishingly long hours: one of the things an i-bank's clients are paying a lot of money for is knowing that at any time they can call up the person who's trying to put together a deal, and discuss it with them. That means that those people need to be around for long hours, which means that the people doing analysis for them also need to be around for long hours. I have never worked in an investment bank and do not know how credible this is.)