Zuckerburg is a bad example; Facebook was his 3rd company, and his second (Synapse Media Player) reputedly got a million-dollar buyout offer from Microsoft. There are many reasons he might've chosen to incorporate as a Florida LLC; the likely one is that past experience with startups told him it wasn't important and could be fixed later, so he chose the simplest option.

Your overall point stands - Google or E-bay would be much better examples, as they really were started by first-time founders.