This may be a quibble, because I think Paul Graham really means a certain type of high-growth startup in mind when he says "start a company". But the rate of new business formation in the US has fallen off a cliff in the past few decades.[1] The number of new companies as a percent of total businesses is 44% lower in 2012 than it was in 1978.
Again, I think this is different than what Paul Graham is talking about. When he says "many more people are starting companies", I think he's thinking more about a SaaS startup than a McDonalds franchise. Obviously that fits in much more with the theme of how people generate massive fortunes. Nobody becomes a billionaire from starting a landscaping service or an auto body shop.
But still, I think it's important to keep the context in mind. In the larger sense, entrepreneurship in America is very much dead. That doesn't mean that it isn't thriving in a specific Silicon Valley subculture, that to be fair makes massive contributions to the broader economy. But it should make us question what makes the Valley so different from Main Street, USA. If not just to figure out how to export the model from Palo Alto to Oklahoma.
[1]https://www.inc.com/magazine/201505/leigh-buchanan/the-vanis...