It's possible they've revised the instructor curriculum. In the NRA Basic Pistol course I took, they taught hammer down on empty chamber for revolvers. I'd have to check if their companion textbook says the same thing. I figured they just kept the old method so that people who are not savy about such things as transfer bars wouldn't go putting a live round under the hammer of Grand-Dads Colt.
Whatever happened to the Western movies?
One potential advantage to an empty chamber under the hammer is that a round can't "cook off" in a fire. My pre-treason S&W Model 66 stands guard night and day at my home. If the place burned, the round in under the hammer could fire and anything down range could get hurt. I store mine fully loaded, but I think about this now and again.