The more I think about this, the more it seems that this test tells us a lot more about gun/grip fit than it does about caliber/recoil. For example, I do not need to readjust my grip at all to fire an entire cylinder of full power .44 Magnum ammunition through my S&W 629 with the Hogue Monogrips that came on it, but I do have to readjust my grip for each shot with .38 Special +P ammunition through my younger brother's Ruger Security Six with the small wood panel grips that came on it. Now, the S&W obviously has far greater recoil than the Ruger due to it's much more powerful chambering, but because its grip fits my hand better, it would pass the test while the Ruger would fail.
Also, it seems to me that this test is only valid for semi-automatic pistols and double action revolvers. I say this because the "plow handle" grip of most single action revolvers is actually supposed to allow the gun to roll up in the hand as this better facilitates recocking the hammer with the shooting hand thumb. Now, some might say that this is a moot point because semi-auto pistols and DA revolvers are the most predominant types of handguns used for self-defense. While that may be true, however, there is a not-insignificant number of people who choose a SA revolver for self-defense and, by John's own description/explanation, this test is not limited to only one use of a handgun. While the person choosing to carry a SA revolver in a large city might be quite rare, the person choosing to carry one into the wilderness isn't all that rare so this distinction, I think, is worthy of mention.