Because there are still a truck load of things that need sorting. They seem to spend most of the time arsing around changing the blades and stuff, instead of adding things that really matter.
I see, it's been a while since I had my 360, what I was trying to say is, they have no real competition, and so can take there time with these updates and not have to worry about it, where as Sony really need to be catching up and throwing the updates out there.