Oh, I think this is a good question.
I thought about it a bit, and like Raini says, I think it depends. I'm a bit on the fence about it though. In one hand, it seems as if jumping is jumping - it's the same stress, same wear, and same damage done. On the other hand, and I'm speaking of jumps probably over 2 feet, the higher they are jumping, the longer amount of time it takes to land. I would think that the larger the jump, the larger the impact on the horse's body. It seems insane to think a horse's front legs and shoulders could take so much impact of a 7 foot jump! I've seen a lot of horses that could jump repeatedly and show little signs of stress on their body - and other horses who are the opposite.
I wish a vet or college could perform (humane) experiments on something like this. I'd be really interested in knowing how the horse's body breaks down and how long it takes. Good post!