The end of the article is more enlightening though.
"Wealthy individuals with lower ability can start new businesses because they are less likely to face the disciplining effect of external finance."
The author also writes that those same correlations occur in business school and other upper tier schools, which lend themselves to perceptions of high achievement.
At no time however have capital costs been low like in the software industry, so perhaps the real key is to encourage more of the low income to hack away :)
Entrepreneurs by their nature have more individuals at the end of each side of the scale, whereas people who work are clustered in the middle.
All a higher average tells you in this case is that when you "win" as an entrepreneur, those payouts are larger than when you "win" in the workforce.
Duh.