I'm not sure I'd agree with that. With the exception of the one job I had in the games industry, the mid sized startups I've worked for gave me the best work/life balance and stable hours. The crazy hours of a young, small startup are well documented, but I also have a friend who works for IBM who has survived several layoffs over the last decade. He managed that because as they downsize his group, he picks up the slack. That often means working 80-100 hour weeks. He does this for years at a time, until he moves departments. Then he repeats the process all over again.

Maybe the sweet spot is mid-sized startups before they grow out of control and large companies who never seem to downsize? Those two situations never seem to last for more than a few years.