Apparently, they removed so much from the game, it could make up another title entirely. Some areas of it including a zoo in an amusement park, Lightning's home, and Snow's "hero squad" Nora's secret base, fully included with missions in it.
I'm guessing it has to do with avoiding the Xbox version becoming 6 DVD's large.
They did say there would be plenty of DLC for FFXIII, let's home some of the deleted areas are included. Although it is unlikely, I suppose, as there would be like 60gb of dlc in that case. It would, however, be a huge chance for SE to make a lot of extra money. They did say they planned for the FFXIII series (including Versus and all others) to last for over a decade.