User blog comment:Yellow Ledbetter/New Assassin?/@comment-112.198.78.141-20120302130533/@comment-4740457-20120302133242

As it has been reported that this game was under-development way before Revelations, so the concept of Hook Blade may not have been there first to incorporate...and i think they added hook blade later on the Revelations as an afterthought when they found out that Constantinople was slightly  sloped and they wanted to add something that could use this in the gameplay.