And if so, how do early stage founders who aren't already rich manage to get by?
On $100k, you wouldn't really be able to save very much, so the idea that you could somehow "escape poverty" while raising a family in Silicon Valley on that salary is somewhat of a stretch.
In Silicon Valley, a "middle class" family typically means two highly educated adults each earning six figure incomes.
Part of the trouble is that income taxes are not based on local economies, so they'd be taxed as if they were quite well off even though they're struggling.
A startup founder is not likely to have dependents so can divide by 4, and then not worry about things like how good the school district is. Although they may not be "rich" in the conventional sense, they likely have an education and connections that the guys who are stocking the grocery shelves can only dream of, and parents or someone else they can always fall back on if worst comes to worst.
It's really a meaningless numbers game - no matter where you live, you have to trim your lifestyle to what your income supports.