Coming in late on this thread, and as a horse lover since childhood I wanted to have my say.
I get really, really angry about this attitude to horses in the Olympics or whatever, there's been a similar thread on Facebook.
Ever heard of the saying 'You can take a horse to water but you can't make it drink it'? Well that applies to jumping, dressage etc. if a horse doesn't want to it won't. As illustrated by the German horse, it didn't like the unfamiliar riders and so wasn't going to perform for them. The response of the coach was utterly disgraceful and she should be banned.
Have you never seen horses that have dumped their riders but continued around the racetrack, showjumping ring or cross country course? This is because they enjoy doing it. My own hated showjumping, loved cross country and hunting and was bored stiff with dressage. Horses for courses.
DD and I were at Hickstead one year when a young and up and coming girl was doing really well with her grey. In front of us the horses bridle fell to bits and the bit fell out of its mouth. They completed the course with the rider using just her legs and voice. Don't tell me that horse wouldn't have quitted given the chance! He was loving it.
I agree with so many of the above posts regarding the domestication of equines. And yes they do now need human intervention for both the gene pool and their well being, even the native ponies. For example, my pony was a New Forest breed, back in the 60s I was able to leave him out in the field all winter, even at night. For many years it has not been possible to leave this breed out at night. On balance horses do extremely well on all counts with their human counterparts.
And if someone comes back at me about foxhunting then I will give them a diatribe on the tragic disease-ridden, starving urban foxes. It's called a cull. Darwinism.