"It's not about discussion" is accurate, but not because Twitter is a narcissist platform. I think it's more akin to sending UDP packets (with no guarantee of delivery to the recipients) than email (with its excessive guarantees). It's even less like mass emails when it's being used like a low-priority broadcast (like when I use Twitter to say I'm headed to a particular bar, my friends are implicitly invited, but with the need to arrange times or RSVP, etc.).

In another sense, Twitter is about delayed discussion. It can set up future conversations that bypass some of the introduction. A friend tweets that he bought a house, he closes on this date, and moves in on that date; the next time I see him we have the chance to jump into an interesting conversation about the house and the process instead of him having to repeat that information for the millionth time.

And there's something else Twitter's done that I'm not sure could have happened before. I wrote a tweet about being in the Salt Lake City airport, and a friend of mine calls me to say "Hey, me too. Let's grab a drink." We hadn't seen each other in a while and neither of us knew the other was traveling or where. That wouldn't have happened a year ago. We would have missed that chance.

(I went a little further than I expected here. But Twitter has some real use cases people are still figuring out, and they're different than email or text or IM or phone calls. People using Twitter for "Here I am! Here's what I think is important! Listen to me." are doing it wrong.)