Ah So Rube
OK, let me modify my statement for Abilene. If the SAA holster, is "molded" to the SAA, the pouch also molds to the Flutes of the cylinder. The Open Top doesn't have Flutes. If the holster is molded to fit the SAA barrel and Ejector Housing, the Open Top Ejector Assembly is longer and and fatter and will "drag" in and out of the holster.
If, on the other hand, the holster is made to a "one size fits all" standard, you wind up with a basically sloppy fit for everything. Which I suppose is OK for some, but I prefer my leather to actually fit the intended gun. Picky picky picky, but atz the way it is. And, I happen to like my Attitude. So There. thibbbbitt.