These are early investors, and most of them not employees. Employees have a bit more time before they can sell their stock, and Mark seems to think that this is just enough time that the company needs to make the investments worth while:
Mr. Zuckerberg went on to tell employees that the press doesn’t know the company’s future plans, and if they did, they would have the same faith in Facebook’s ability to fulfill its lofty stock-market valuation. He said that investments the company has made over the last six to 12 months will soon bear fruit, the people said.
Guess it is going to be an interesting year for Facebook.