An interesting counter point, VC's as an industry average significantly lower ROI than the boring old S&P 500. One way to look at the VC industry is to realize VC's can make millions even if there portfolios have negative ROI. What they need is to manage lot's of money and being in on the ground floor of the Next Twitter buy's lot's of credibility.

In that context, a company that reaches 50 billion in 30 years is far less valuable to a VC than a company that hit's 10 billion in 3 years and then goes bust in 10 years.