From Dan Cohen, “Back to the Blog“:
It is psychological gravity, not technical inertia, however, that is the greater force against the open web. Human beings are social animals and centralized social media like Twitter and Facebook provide a powerful sense of ambient humanity—the feeling that “others are here”—that is often missing when one writes on one’s own site. Facebook has a whole team of Ph.D.s in social psychology finding ways to increase that feeling of ambient humanity and thus increase your usage of their service.