As the elite skiers advance on the boat the handle has to start moving to the inside in relation to the ski path, otherwise the ski gets blocked from its swing. The only way you can do that while staying connected ends up with the inside elbow bent. It's a byproduct, not an action. In those pictures of Nate, that outside arm(which is straight, or as straight as you can really expect) is the connection to the boat. Once you're at that level you can use that handle as your means of varying the tension in the line. Mere mortals should not be even thinking of those types of things because it's the tail wagging the dog. A guy like Nate, CAN do that because he's done so many things right up to that point.