I recently contacted the Ubisoft's support for information about this DLC for Assassin's creed 3, which is currently only available for PS3 and they told me that his release on Xbox live depends on you, so the question is: will you release on Xbox live this DLC? If not, why?
Looking forward for your feedback I offer my most cordial greetings.
Ubisoft answer about this:
Thank you for contacting the Customer Service for assistance Ubisoft about Assassin's Creed 3.
Unfortunately, Microsoft is the only one who so decides and not made availab at least for the moment the dlc. You can contact them and ask about any news.
Because it just depends on their choices are not informed of these choices.
Looking forward to its eventual stop, I take this opportunity to extend my most 'best regards,
Technical Assistance Centre Ubisoft