Just like any book from a series, hooks are implemented to allow the story to go forward in the next book. Simple. The fact Bungie implemented the hooks for elements they know will be released at a certain point in the future is no different. Besides that it also reduces the download sizes of DLC, since they can now avoid you having to download new versions of core parts such as the map and the geometry used to enter new areas (hooks). If you want to whine about not enough content being offered upon initial release at least have the balls to be upfront about it. These findings are like finding a mare's nest.