I mean, what problem does FarmVille solve?
Companies like AngiesList and Groupon serve a broader market and are not based in SF area. So, they get less attention. But, these are bringing in far more revenue and will likely last longer.
Just because there's people that use Groupon-like utilitarian services doesn't mean that they won't have fun with other stuff too.
I think Facebook is moving to prevent someone else getting any sort of a foothold in the social media space.
It's play essentially amounts to little more than "you don't need to look at FourSquare, you can just stay here with us". If it turns out to be popular great, if not then it's not fussed, but what Facebook doesn't want is someone else building up a user base with anything close to critical mass.