Yeah, while I don't think the purpose of the body scan is ENTIRELY cosmetic, they definitely made it something you'd see during the demo for a reason:
"Wow! This game judges shoulder span, can tell the angles my arms and legs are at if I move them ... this Kinect stuff is incredibly deep! The future is now!" :)
In reality, it probably doesn't do much with that data other than determine a good distance away from your body to put the 'selection' icons, and possibly use in determining if your body parts are at a proper distance or angle to get "percentage credit" for doing an exercise routine correctly.
They don't save the information and let you view it later because you'd see it's not fully accurate at that point.