Yes, I'm in Romania, but I've been working exclusively with Sillicon Valley companies and have been working within startup environments for the last 5 years.
Being able to say NO is not a matter of where you work, but rather one of actually saying NO. It may not work well of course, your managers and peers might not like that, the secret being to not be at the bottom of the chain - as in, you have to be reliable and capable and work on hard enough problems as to not be easily replaceable. If you can prove that you're as good or even better than somebody doing overwork (which is entirely possible because of the reasons I outlined), then nobody will mind, as in the end it's all about the value / artifacts produced, not about the lines of code written and not about the number of hours worked.
And in my oppinion, if you can't produce value while working regular hours, then working overtime won't help anyway. And if you can't produce value with overtime, do you think your boss will keep you hired just because you're a "hard worker"? The market really doesn't care about that and your boss/manager would be an incompetent if he thinks otherwise.
Speaking of market forces, it's a mistery to me how you Sillicon Valley based developers, that live at the horse's mouth so to speak, can't easily switch to jobs that you like in case you're working in environments full of jerks. I mean, even if everybody expects you to work overtime or to do things you don't like, you can always build your own startup for Christ's sake, something that I (being outside of the US) can't easily do.