The Exchange analogy doesn't apply to Twitter. For starters, most people want to keep their Exchange email confidential. IOW, the rest of the world can neither

The Exchange analogy doesn't apply to Twitter. For starters, most people want to keep their Exchange email confidential. IOW, the rest of the world can neither see the contents of the "inbox" nor the "sent mail" folders. OTH most people want their twitter status updates to be seen by others and there isn't much incentive to host it securely.