Presets are just a set values that are saved out to be re-applied later. Think of your car radio presets…you save out an FM station with the value of 99.7 so you don't have to dial it up again. You just hit the preset and it dials it up for you.
DAZ Studio presets offer the same convenience. Almost any value can be saved out and used later. If you create a preset for a pose where the “right elbow” is bent at 90º, that preset would work on anything that has a “right elbow”. If you tried to apply the preset to something with an “r_elbow” nothing would happen. “right elbow” and “r_elbow” aren't the same thing.
When an artist creates a preset they assign “compatibilities”. In other words they tell others what the preset is designed to work with. In many cases a pose preset may work “OK” with many different characters but it should work perfectly with those characters that are “compatible”.