"Prior to the internet, the differences in communication between community and audience was largely enforced by media -- telephones were good for one-to-one conversations but bad for reaching large numbers quickly, while TV had the inverse set of characteristics. The internet bridged that divide, by providing a single medium that could be used to address either communities or audiences. Email can be used for conversations or broadcast, usenet newsgroups can support either group conversation or the broadcast of common documents, and so on. Most recently the rise of software for "The Writable Web", principally weblogs, is adding two-way features to the Web's largely one-way publishing model."
Clay Shirky: Communities, Audiences, and Scale