It is photos such as this one that give African Lion Safari such a bad name with certain journalists in Canada. Asian elephant balancing on circus-like platform...hmmm.
This kind of tricks damages the joins of an elephant and will likely cause arthritis later in life. I am not aware that dolphins get sick from doing their shows, in contrary. additionally, George is a male teenage elephant and bulls much younger then him have killed their trainers. The guys in that zoo are asking for trouble by continuing this sort of training with a male in this age.
Another question is how much of "enrichment" it is for such an intelligent animal to do exactly the same show with exactly the same tricks every day for years and years. In my opinion, that`s nothing but boring for the animal and has nothing to do with enrichment (which should anyway encourage natural behavoir, which standing on the front legs is not!).
Just think it breaks the monotomy of being in the exhibit all day, is a bit risky with a bull though. But can we not start another debate on animal performance, we already have 2 or 3 as it is.