I think it is shift in focus that is the root cause of this issue. There are plenty of avenues for online gambling as well as real ones, where they extract money out of the wallet.

However, the question is in exchange for what? As long as the focus is on the entertainment quotient I think these businesses do just fine. The moment the focus of business shifts to just extract every possible dollar out of its users, people get smarter & just leave. This is probably what is happening with Zynga.