The reasons you give are all valid reasons. However, you miss the reason most likely to sway end-users: a shortener service can relate every page a user has see

The reasons you give are all valid reasons. However, you miss the reason most likely to sway end-users: a shortener service can relate every page a user has seen to that user (or at least, to his ip). The privacy angle is the biggest factor imo. In your info page you may also want to promote Untiny (http://untiny.com/extra/ http://untiny.com/extra/) as a service which helps bypass shorteners with minimum fuss.