User blog comment:D. Cello/Assassin's Creed: Revelations (PC) - Official Assassin's Creed Wiki Review/@comment-187.105.170.237-20111216164754/@comment-1153722-20111216220316

In the teaser, you can see that it initially wasn't supposed to be first person. Ubisoft probably scrapped the whole third person concept because of lack of time.