There is a HUGE difference between the cavalry example BSMS showed and the people riding banks like the hickstead bank.
Firstly, they do no hurl their horses down them at top speed. Their descent is slow and very deliberate. Macabre, have you ever watched the Hickstead bank ridden? Yes, horses sometimes fall, but the speeds and forward momentum are minimal and few bad injuries occur. Even this extremely aggressive rider rode the bank carefully http://www.dailymotion.com/video/xjl...ed-derby_sport
Secondly, these horses are doing these things ALONE. There is no chance of being pounded by other horses who are also being thrown down this hill.
Thirdly, these is just not the same wanton disregard for the health and safety of the horse.
This race is a sad example of just how much some people can forget about their horses health...all for money and ego.