This is bonkers, because Activision Blizzard alone are making money hand over fist with WoW. There's no way that Zynga is worth that much.
Dont undererstimate the gaming market.
Stocks tend to be valued based on future earnings more than present earnings - after all, if you know that a company will be making more money next year, it's rational to buy their underpriced stock today and wait for it to appreciate.