They have the natural inclination to learn the gaits, due to their Ancestors the Narangansett Pacer, but thanks to the strong influence of the Thoroughbred they are predominately trotting horses. There are a few "naturally gaited" individuals but they are very rare and not sought after or bred for. The "Five Gaited " American Saddlebreds you find were taught how to do the extra gaits. If they do not look like they will be successful as a Five gaited horse, or are not built for it, or look like they would be successful in another area, or for any number of other reasons, they are just not taught. You can get a gaited one fairly easily, it just had to be taught, unlike, say a TWH who are truly a natural gaited horse, born doing it.
Here is a neat video that the ASHA did for the WEG. The American Saddlebred - All American Athlete - YouTube Posted via Mobile Device