The structure of the company gives you the right to future dividends at the same rate as other classes of stock. So as long as they think they're creating something of value and the marketplace does you own an equal equity share of that entity.

Google finally paid a dividend (although a one-time dividend) and also announced a stock buyback so these companies may start returning capital. As of right now facebook thinks that capital is best put to use inside the company. I think there's a pretty good chance they're right on that.

Bottom line, you have the same rights to payments per share as Zuckerberg. Also technically Zuckerberg will at some point (might be 30-50 years from now) start divesting his shares and at some point your stock might be valuable for someone who does want to change the structure of the company or take it private.

Another defense is "internal arbitrage". So the company has value, and a different owner might decide to sell off assets or pay dividends to realize that value. But even without the stock changing hands, let's say it started trading at $20 a share. This would encourage Zuckerberg to work with a PE firm to take the company private again.

When stocks trade near, at, or above fair value you wont' really see any of these things happen, but if they started trading way below fair value, you would.