I've always suspected that Dave had intimacy issues ;-) but seriously, I agree with the stated problem but see it more as an opportunity for Facebook vs threat. I think by focusing first on casting the widest net possible for capturing the social graph, and then enabling the platform for applications to be built underneath, they've prioritized appropriately. I'm sure they recognize this problem (thus the new Groups feature) but also realize that 90% of the development effort towards solving this problem will likely be built on their platform.