i've been trying to figure out the same thing and this is what i've found.
a gaited saddle for one has a deeper seat because when a the horse gaited it doesn't ride horizontal it rides more at an angle, the back end is closer to the ground than the front, the more the horse reaches under itself the greater the angle the horse rides. So the deep seat is designed to keep you from falling out the back of the saddle. second a gaited saddle has a high tree, though this depends on the saddle. the high tree is for high withered horses and it also alows the room the horse needs to pick it's front feet off, however this is more for a show horse if just trail riding and light showing, that doesn't require the horse to lift its front feet up high, then a high tree isn't required.