You aren't describing communities, you're describing subjects.

Any number of people follow John August and Jane Espenson. None of the people who follow both Jane Espenson and John August can talk to each other using Twitter - because unless they follow each other, they don't see anything unless Jane Espenson or John August retweet it. It's a truly one-way communication system.

Now suppose people who follow John August and Jane Espenson also subscribe to Done Deal Pro or whatever that thing of Coppola's is called. They've got forums where they can actually interact without the intermodulation of John August or Jane Espenson.

Follow Kevin Spacey and Beau Willimon and you have Kevin Spacey and Beau Willimon's tweets. Subscribe to /r/houseofcards and you have a community.

It isn't a community because it isn't a community. There's more community amongst CB radio users - at least everyone can talk on the channel. Twitter is, at best, a targeted search. Unfortunately, since it's artificially limited to a nothing-scale message, it's a targeted search with which to find other search terms, nothing more.

Followers? Followers are nothing. I created a twitter account for the sole purpose of off-loading my Kindle bookmarks. I've used it four times.

It has 52 followers. I'm going to guess 52 of them are bots.