If Uber is like the other unicorn companies, the investors that gave it the massive valuation have shareholder agreements that allow them to get paid before everyone else does. Anyone with common shares (e.g. employees, etc.) would get virtually nothing.
And if there have been multiple rounds at multiple valuations, then multiple agreements and/or complex negotiations. It seems logical that the principle is that the outside world just isn't going to know the ratio of optimism to desperation in a high valuation - since saying "You're buy at a high valuation" is equally saying you "get the money for a low valuation first".
