What I can't understand is why Twitter itself hasn't implemented this functionality. They could just have an "add link" button which exposed a text field for a

What I can't understand is why Twitter itself hasn't implemented this functionality. They could just have an "add link" button which exposed a text field for a URL, which is then added to the message. They could then charge for metrics on the clicks. Why encourage the use of a middleman? They could build it such that they could at least keep the proper href, maybe rely on a script or device API to count clicks. Best of both worlds.