Star Tours has a fairly straight-line motion (ie, you're always moving forward), even though you do alot of up and down and side to side. You don't ever go backwards or completely stop.
On Body Wars, you are moving along with the blood being pumped through the body. It's a stop and start motion and, it seemed to me (although it may have been just a feeling, rather than actual motion) that you sometimes even moved backwards a little. Put your hand on your heart and imagine being pushed along by the beating.
I found Body Wars made me sick. I've never had the problem on Star Tours (thank goodness, since it's my DD's favorite and we ride it more than 10x each trip).