"I'm not sure that this is all 
  that relevant, really.  I've seen horses killed during showjumping 
  tournaments, killed at eventing tournaments.  I've seen dressage horses 
  put down at ten, lame for life because they were pushed too hard, too 
  young.  Endurance DOES place huge physical and mental strain on the 
  horse, I agree with you 100%, but that doesn't make it "unique".  What 
  makes it unique, in my (uneducated) opinion, is that "winner" are very often 
  not the most talented horse on the day, but the best-prepared, and very often 
  it's a team which wins, not a horse.
  Howard said:
  If you start throwing money into the sport, like they 
  do in your sport, Karl, it won't fly with endurance. 
  It will, Howard.  
  Whenever you throw money into a sport, you'll attract people for whom the 
  "purse is all".  That's the nature of people, I'm afraid.
  The only sport, perhaps, where 
  this WON'T happen, is probably dressage, because I've found that most of the 
  money-driven people are also adrenalin-junkies, who like to get their kicks 
  from the dangers inherent in the sport.  I have no stats on this, it's 
  just a gut feel.