Many of us have done exactly that, it just takes years of planning and being fortunate enough not to have severe medical conditions or loves ones you need to take care of with all of your finances.
Again, most people would much rather tell themselves that the reason why they're not entrepreneurs is because they're not Bill Gates rich, rather than making the sacrifices most entrepreneurs have to make to get things going.
Your idea of "saving money for when you quit" doesn't work for middle class as the amount you save is not enough for "living on ramen for a few years" -- it will likely not be enough to even pay rent.
If you were earning more than 100k you were in the top 7% (in 2014)
More than 75k puts you in the top 13% or there abouts.
Tech is wealthy
100k in Dallas is a different conversation though.
Literally the argument the article is making!