They arent able to add vault space because they CAN'T PHYSICALLY ADD VAULT SPACE. It is tied to the tower, and the tower cant be any bigger than it is, the last gen systems can't take it. They could do things like make it a separate memory array and load it in, but I have a feeling they don't want to -blam!- with stuff like that and potentially cause everyone to lose their weapons when they could be doing other things. Don't buy into that PR garbage that DeeJ says. Always listen to the developers, ignore DeeJ.