As far as I know the only trigger style ABs are an Iwata and the Tamiya. So most of us merely bought the most common style. I, for one, have never even seen a trigger style except online!
Yes, I know that Badger makes the Model 400, but that is really a small pneumatic spray gun for large scale work like murals, R/C aircraft and detail auto painting.
edit Ya know something? I should have looked up the model 400 before spouting! It's a third style in that it has a "paddle" like handle that you use with your thumb! /edit