Given the basic necessities for a social group to form, it often takes awhile for it to do so, while removing these necessities can kill it very quickly. CMU shows this general tendency pretty well - losing the CSLounge, shrinking of the cluster, etc. Now GHC has a *lot* of open space suitable for that kind of stuff, but new traditions, particularly of the organic kind, will take a bit to form.
It's interesting watching it happen, both in the more manual "let's start doing this" sense and in the "it just sort of happened" sense.
It's even more interesting that the space itself is obvious (as we "figure it out") - it's more about figuring out other people and what herding is possible.