The main questions should be: "How can people successfully close a viral loop?" And "Wh would people come back?"
"Why would people come back?" is usually correlated with recruiting awesome co-founders, talented employees, great mentors, influencers to talk it up, and top tier investors. Then, the company has the time and resources to discover the best answer to that question.
Maybe once in a decade there's something like Facebook, which just explodes out of the gate instantly (and just buys the better .com later). But I wouldn't want to bet my company on that... especially when I can just spend an hour and brainstorm a .com to address the problem. Anything less is a failure of creativity.
I remember writing about it four years ago: http://qbix.com/blog/index.php/2011/03/phase-1-successful/