My sense is that the people in charge of Facebook are happy to take big risks with their company, and I don't see why they shouldn't.

Whether the company sells now for $6 billion or tanks and sells for $600 million in a few years, they'll have a lifetime of riches. With money a less important consideration, the question becomes which would be a more interesting activity for the next decade: Building a globally powerful company that fundamentally changes how the internet game is played...or becoming idly rich?

Financial risk/benefit calculations are much different for an individual than they are for a large corporation.