It's completely up to the dev. Putting about 30 seconds thought into it I came up with two decent options - leaning (it's already been said, I know) or the position in which you stand - when it loads up, the distance you are from the tv is the neutral position, stand closer and you walk forward, stand further and you walk backwards
The companies using Natal are going to put thousands of man hours into picking and optimising their method.
All will be fine







