You know I half wonder if they'd do this so that the more popular clients don't roll their own service. While I've watched Facebook run with the ball in the last year or so it feels like Twitter hasn't done anything new or interesting. The one thing that Facebook has gotten better at is giving their users more context to have richer conversations with each other (by adding Friendfeed, having robust games, etc.) while Twitter still feels like MS-DOS. They really need to do something to make the whole experience richer...