I am speaking out of experience. I've done advertising on games that have been played 100 million times around the net, and I've tried directing that traffic back to my own site and profiting from selling games directly. The latter is obscenely more profitable, both in my experience and that of everyone I know.
In terms of success? They took VC and grew very well, we bootstrapped our way to 5 employees without taking a dime. Total investment under a thousand dollars and profitable after a few months. In terms of raw game play counts, I'd bet money on us being ahead.
All in all, I'd rather be in their position not mine, but I guarantee you, the strategy outlined is not the reason why. And their greater success does not mean that I should not be allowed to have an opinion on what I've been doing successfully myself for years!
By the way, if one must always learn from more successful companies, it would be hard to argue the case for Zynga to switch their monetization strategy over to ads.