I don't think this really benefits users all that much from a privacy perspective; it really just consolidates tweet link clicks in server logs.
The information that would normally go in the referer header would presumably be available via future t.co APIs (although there is some privacy protection there now).
Posters can still use bit.ly links (just not by default); they would actually have a t.co link to a bit.ly link to their actual link. t.co links may offer similar statistics in the future. Twitter is also a private company that can track a large portion of peoples' browsing history.
The information that would normally go in the referer header would presumably be available via future t.co APIs (although there is some privacy protection there now).
Posters can still use bit.ly links (just not by default); they would actually have a t.co link to a bit.ly link to their actual link. t.co links may offer similar statistics in the future. Twitter is also a private company that can track a large portion of peoples' browsing history.