Just my two cents on this subject. Anyone who claims to have a spider with ZERO wobble either doesn't know what to look for, hasn't had the snake long enough, or doesn't pay very close attention to the snake.
Pretty much just like everything else in the world, when something is different then the norm, people automatically assume there is something "wrong" with the snake. In the case of the Spider Ball Python, I think this couldn't be further from the truth.
I have no studies to back this up, it is only based on my personal experience. Spiders have wobbles. They also tend to be some of the strongest eaters, and some of the best breeders. When holding a spider I think there is no doubt that they have a different personality then any other morph I have held... and that is certainly a good thing.