I don't know... but those are the very reasons I've decided to get away from Western riding and go with an English discipline.
I was recently ring steward at a multi discipline show. I got to see the horses "up close and personal" and hear why the judge choose one particular horse over the other. I've also shown WP (at a VERY small show) and know that my horse is expected to move at a snails pace throughout the walk, trot and lope. I also know that my horse simply WAS NOT BUILT to travel at that pace. He does, however, have a natural low headset, though no where near some of the "peanut rollers" of past (and sometimes present) WP showing.
The barely moving, shuffling "show trot" on WP horses simply does not look natural to me. I prefer the collected, more natural look of the English horse. And this is coming from someone who's been riding western for 20 years.