Sure, but this an obvious "correlation is not causation" situation and the reason for this is unpleasant.
If you're from a middle-class background, you have to take full salary because that's the only money you have to live on. If you're from an upper-class background, taking full salary hurts your relationship with investors, and will possibly hurt your bargaining position in future negotiations.
People from middle-class backgrounds cannot afford to pay themselves under $50,000 per year in San Francisco. As for the upper class, if they have trust funds, they can and probably will accept low salaries, just as there are publishing interns all over New York, making what would be poverty wages, and who live on their trust funds.
People from upper-class backgrounds are more likely to have the connections that will make their startups succeed.
That is the reason for the correlation. It's just another incidence of (unintended?) VC classism.