Lurkers Are Not Part of the Community
Lurkers are fans, they are not participants; however, they could become participants if the system encourages it, like how Slashdot does with their comment rating system.
Clearly, some things do not foster community. You do not need a real identity, but you need some identity. You need to have a voice, a reputation, a presence to be part of a community, because it is (at least) a two-way propositions. Thus "lurkers," people who only read or listen, are not really part of a community. They may fancy themselves to be, but no one would miss them if they left. They are fans, not friends. Lurkers may latch on to a culture, but they do not contribute to it. (That's why fandom is so eerie: There's usually no real communication between the fans and the stars, just lurkers and fantasies on one side and a PR machine on the other.)
Esther Dyson argued that lurkers are not part of the community, they are fans, people observing the community. This would imply that Twitter users can be simultaneously lurkers in some relationships and community members where two users follow each other and use @reply with each other.