Riders who entered the XP2001 had different goals.
Some riders had 4 horse trailers full of horses to condition. Others switched horses mid ride. This ride was a great conditioning event.
Some riders such as my Son, could only get one month off from work, and so could not complete all 2000 miles of trail.
Some riders only rode 25 miles a day.
Some riders rode as fast as their horses could go, trying to capture a "Win," or in some cases the "Best Condition" was the goal.
Some riders had the Tevis as their goal, which was run only a few days after the completion of the XP2001. "Zane" was one of these horses. He collected so many "Best Conditions" during the summer, and running very fast at the same time. His owners left the race a week or 2 early so that they could prepare him for a maximum effort at the Tevis.
Other very excellent horses had the Pan Am Race as their goal, and only used the XP as a wonderful conditioning ride, but took days off to rest the horse, remembering that the Pan Am Race was their bigger goal.
It is very hard to answer for anyone else, so all involved, please forgive me if I am not totally correct on all facts.
John, the rider of the Icelandic had 2 with him. I believe that he would have used both and split the mileage between them. One developed a problem, and so all the miles fell on the other. John is most cautious of the well being of his horses. He rode them slower than almost all of the other riders. Each day John walked many of the miles leading his "Wonder Horse" to ensure his well being. What a team!
Still, there were many other horses who could have walked, or traveled the miles at the same speed as John did, it was just not the goal of the riders to do that.