Did you even read his post?
Yes, and I'm sticking with my point. If he's not offering something valuable enough that he can charge enough for his time to tolerate not being paid for a week here and there, then he needs to become more valuable, or find a customer that can afford him. Just as true for contractors as it is for traditional employees.
The market is broken because of a lack of supply
You've got this completely backwards. The market is working - it's establishing a value for the skills in question, and the GP isn't liking that value precisely because there's too much of a supply and not enough demand. He needs to go to someone who has demand, or go where it is, or offer something that's more in demand. If he does, he'll find the market works for him, just like it's supposed to.
inflexibility due to, you know, life and family
Still the market, working as expected. If he values those things more than he does bringing home more money, than he can't complain - he's the one establishing the priorities. Why should someone else make it their priority to match his goals, rather than their own? Especially when there is indeed a huge supply of people willing to do the same work, many of them who aren't putting other priorities first. It's a value analysis for everyone involved.
but reality isn't like that
It is if you want more money. If you value staying put for your kids' sake, then you've just made a value judgement, period. That's reality, working.