His point isn't anything more than "Only a small proportion of people will be successful startup founders." We know this from experience and intuitively, because it's hard to start a startup and succeed.

The problem with his "argument" is that it's completely arbitrary. And I don't mean the 80/20 part, although that is too. He applies the 80/20 rule an arbitrary number of times. Why not one fewer? Why not four more times, which would get the number of startup founders down to 2.5? I can easily make up four more statements justifying the application of the rule.

Agreed....and I generally enjoy the article listings on Swombat too. Nothing wrong with the application of the 80/20 "rule" here. No way to determine the actual numbers but as a thought provoker 80/20 is just fine.... and an identifiable concept many are already familiar with.