Very true. That is because the more energy put into the shot, the more you get at the receiving end. Gas-operated semi's use gases, of course, to operate the bolt. That takes away from the energy going into the shot, therefore explaining the less recoil.

That brings up another thing I would like to point out. If you shoot a semi auto for a while, then switch to a pump, the first shot with the pump you will notice the huge recoil difference.

Once I've gotten used to the pump's recoil, I don't notice it until I fire the third consecutive shot.