Indeed. There's absolutely no need to include it. The whole point of the Kinect port on the "S" is so that you only need the one cable.
EDIT:
I've just read that story at Joystiq. What a pointless piece of "news". Why on Earth would MS include the AC adaptor with Kinects that come
bundled with an "S"?
If someone has purchased a Kinect & 360 "S"
bundle, what use would the AC adaptor be to them?