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.
I'm not against doing some extra time if needed, but working overtime regularly with the 'I like my work' mentality is for me the wrong way of thinking, since anything you could be doing sitting at a desk for your employer outside the agreed hours you could be doing it for yourself.