If you pay attention, you can count three to four+ different Diablo's during the half-hour TV show. That isn't counting the two used in the show's introduction. They didn't bother trying too hard to make the pinto horses look alike.
Pancho probably rode several "Locos," but it is more difficult to see the difference.
PS-I read a post below titled "Horses" stating that they noticed the ever changing horses as well.