The tweet still needs to fit into 140 characters, including any metadata you want visible to the recipient. Think SMS.
Hence, might as well make it a user-manageable item in the tweet itself.
Hence, might as well make it a user-manageable item in the tweet itself.
And for my money, the reason they wrap every link through t.co is because this way they have analytics on every link clicked on Twitter. That sounds pretty valuable to me.