nteresting visual, although I think it ignores the concept of synchronicity as a measure of interactivity. for example, in a real conversation, one person speaks and the other responds. with a letter, on the other hand, one person "speaks" but even aside from the delay in transmission, the other person has control over when he or she replies.
using this basis of comparison, the items can be categorized in three ways. conversation, video chat and telephone achieve the highest level of synchronous communication. messages - instant, text, facebook or twitter - have the potential to be synchronous but do not have to be. facebook status updates also fall into this category (although communication by status message seems rather impersonal!). email and snail mail correspondence, while arguably more private, cannot achieve the intimacy of synchronous communication.
I would also argue the categorization of twitter messages as broadcast (one to many) when those getting the greatest value from the service are using it as a conversational medium. those conversations may be public, but they can still be very personal...