I realise that Johnny meant this as a joke:
But, why not? If there is one Zynga universe in which you have one wallet but lots of different ways of earning cash (via different games), are people more likely to play two games? They currently just try and spam you into doing it. I must admit here, that I am mildy addicted to Farmville. I find a Cyworld/Habbo-like pleasure in my little farm. Yes, I'm sad. You never have to speak to me again.