As a bootstrapped company I understand what you mean, but that doesn't mean companies like that cannot succeed. ie. Google, Yahoo, Facebook, Digg, etc.
According to Zuckerberg, Facebook already had thousands or hundreds of thousands of users when they took funding, and they were funding growth with ad revenue.
From what I've heard, they took funding primarily to build the photos app, which ended up being FB's killer feature over other social networking sites at the time.
One of Zuckerberg's Harvard friends, Eduardo Saverin, funded the company early on. Eduardo had good luck trading futures to the tune of several hundred thousand dollars profit.
