I don't want to put words in his mouth, but it sounds like David is arguing that should Zuckerberg decide to just walk away from Facebook today, he would have a very difficult time coming up with $6.9B in cash in exchange for his equity. (Not to mention if other equity holders wanted to liquify at the same time.)

It is important to point out however, this a valuation does not make. Liquidity is not part of the equation.