With coders, that's clearly not the case right? Coding requires immersion. Same person working on same thing 60 hours per week will make a lot more progress per hour than if he worked 20 hours.
In the freelance world, this is name of the game: recruiters want people to work as much per week as possible for this reason, freelancers want to work as little as possible (that improves their skills quicker by working on many things at same time, plus provides job security of having 3-4 clients at same time so they are unlikely to all fire at same time).
Some kinds of coding do benefit from lack of interruption, so that's can be an argument for very focused work. But one way coding is different than, say, factory work or service work, is that our errors accumulate. It takes just seconds to put a bug in, but hours or days to take it out again. So anybody working long enough to get tired will very quickly hit diminishing returns. There's a nice presentation on this from a while back: http://www.lostgarden.com/2008/09/rules-of-productivity-pres...
I also have come to be suspicious of the "hyperfocus for many hours to get large amounts of state into my head" approach to coding. Code I have to be extremely clever to write usually ends up being a giant pain in the ass to maintain. These days I think it's better to use things like unit tests, pair programming, and very frequent releases to get things done.
In the freelance world, this is name of the game: recruiters want people to work as much per week as possible for this reason, freelancers want to work as little as possible (that improves their skills quicker by working on many things at same time, plus provides job security of having 3-4 clients at same time so they are unlikely to all fire at same time).