Working beyond 40 hours is non-productive is a rhetoric I see often on Hacker news. And it always blows my mind. My life experience has been exactly the opposite.
The parent article does not state it as a requirement - more so as a nature of reality for the more ambitious folks in the startup vs. corporate category. I find exceptional folks in my company to be also very hard workers - by choice and not by force. And there are plenty who live a precise 40 hour schedule. Which is fine for both parties as long as that's what they want. What I find pretty ridiculous is the very common new-agey declaration that there is only one right way for everyone which is "40 hours of work" and anything else is just a waste of time. I think it is a very appealing life-style for many - but not a reality for many people who want to get ahead in their careers, are ambitious or are attached to the nature of their work. I see nothing wrong with that.
This may be a "dangerous" thing to suggest, since I realize it edges on a "if no one does exceptional work we all look fine" mentality which certainly isn't productive, I just mean to stress that buying into 40< hours may have ripples in terms of legitimizing it as a Carte Blanche system, (Yes, this is a slippery slope argument, but having seen it pan out as I've described I'm less hesitant to lend it credence.) and as you say, an appealing life-style for many, or some, certainly might not be for all.