I think that what has changed is the amount of information that a reader/writer has access to. For instance we can safely assume that most readers/writers come to a site with knowledge about the information item "New York". If we just have the information item "New York" in a tweet the reader has a good idea about the information that is contained in "New York" as well as other related information items that can be associated with "New York"

Twitter and other micro information services work because we have come to a point where readers/writers have access to any needed missing information.