Surprisingly enough... there is no set rule here. Some people have trouble doing both, others manage both just fine. I would guess there is a correlation between those that really want to achieve both and those that do. Are we going to assume because a few successful people don't have a typical family life that this is because they are successful... and not because they didn't want a typical family life? That seems like a more obvious explanation to me.
So often we look for simple rules as an explanation, but typically outcomes are a result of many smaller factors. It's like the recent discussion here about VC causing more startups to fail vs. succeed. Maybe we can realise that VC isn't the deciding factor, in fact there is likely no single deciding factor, just a bunch of things that impact the outcome.
I agree there's no one solution for every situation. But it is also important for people to realize that it is possible to balance family and start-up needs.
Startups can provide flexibility, especially in working times and telecommuting options that larger businesses usually cannot. That flexibility can enable you to spend the right time with your family and still meet the demands of a startup (which you shouldn't underestimate).
I agree it's possible to balance, I do so myself. I do however suspect that the benefits of startups you mention are more for employees of startups than the founders.
So often we look for simple rules as an explanation, but typically outcomes are a result of many smaller factors. It's like the recent discussion here about VC causing more startups to fail vs. succeed. Maybe we can realise that VC isn't the deciding factor, in fact there is likely no single deciding factor, just a bunch of things that impact the outcome.