Federation makes a lot of sense for a micro blogging service, as no community is the same. Allowing for different rules and styles of moderation without trapping users in silos / walled gardens, is exactly what we need in the social media space, in my opinion.
Of course it isn't, the big question is really whether it should be, since network effects mean it's much harder to compete with established social networking sites/services.
Still, I do hope Mastodon does well, since a federated Twitter esque service makes a lot more sense than a centralised one, and feels far more in tune with what the internet should be.