What you have to remember is that top AAA games take 3+ years to develop, whereas top zenga games take 6 months and generate just as much revenue. The risk factor is far, far lower for zenga, and that makes great financial sense :)
Sure, but Zynga also needs a couple of games to reach the revenue of a Top selling AAA+ title. Of course its more risk per title but what i am just saying is that there is also alot of money to be made with the classic gamers.