yes, i've found this as well. the reason is that employer-based constraints on your schedule are always arbitrary, rarely compensated for in full, never equitable across power structures, and only tenuously negotiable in your favor.
in other words: your life becomes theirs to control in spirit, if not entirely in practice. it doesn't matter if they expect you to be at work from 9 to 5 or whatever else. if your employment is contingent on holding their schedule, they effectively hold control over the rest of your life's schedule.
and they excercise that control to the detriment of your life as a matter of course, routinely, ruthlessly, without hesitation, and without consideration, in nearly 100% of cases -- yes, even in the "cool startup" you're working for.
remember, you need to ask them to take time off to care for your sick relatives. you need to ask them for permission to not be at work to spend time for yourself on vacation. you are explicitly their property for however many hours per day, but they also own enough of you to implicitly dictate where you're allowed to be and when, and for what reasons.
i guess some people find it a good bargain to trade their autonomy for a wage. it's very hard to respect that kind of thinking a lot of the time, but i've learned to do it simply because most people accept the bargain and it'd be too isolating to behave otherwise. for me, it's an intolerable situation to bear, even for a moment.