I don't think there is any such barrier. I've read multiple articles from multiple publications about the same Marissa Mayer, and they all have the same anecdotes and themes. If it's so consistent across multiple publications, you have to think she really does say all these things. Whether she walks the talk is another question, but she's probably a freak of nature who is really able to do so.
Moreover, the legend of the über-productive employee who never sleeps is a double-edged sword and can demotivate the employees that person touches in ways that far outweigh the direct positive impact to the company that person has. As stated above, it's one thing to work 12-16hr days during start-up phase, but if you're doing it as a matter of fact when you're a 30,000 person company, frankly you're doing it wrong -- even if you're the founder, owner, board member or C-level executive. Leading via exemplary personal performance and ethics is one thing; driving those values throughout the organization is far more important.
