As speed racer said, that was probably a lower level. I find they do move a very little bit more then hunters when the horse is not collected because the saddles let us have a deeper seat, and when the horse moves, well, we have to move with him. Once you get to the higher levels, and the horses are more collected, the riders will probably move less because the horse is more collected, trust me, with most horses, when the horse is in front of your leg and more collected, it is soooooooo much easier to sit still. and when they get to the higher levels they are better riders as well.
If there are no horses in heaven... im not going.