172R. Vso is 33 kts. Then I checked the 172S. Vso is 40 kts
Yes, I agree with you! The POH charts tell us that the 172S is 100 pounds heavier than the 172R. Aside from the weight change, I doubt that the engine and prop affect the stall speed. Interesting though, as stall speeds are accurate in CAS rather than IAS, note that there only 1 knot difference in KCAS stall speeds in that configuration between the two 172's!
I've done lots of stall testing in many models of Cessnas, including lots of mods like STOL kits, floats and external loads, and some AoA system set ups. CAS becomes a pretty important factor, when you're really getting down to the precision of the stall speed. That's why the POH says that KIAS values are approximate.
Rather to realise that energy management by speed is another tool in the toolbox.
Yes, it is. I don't deny that what you suggest works. But, I opine that it's a tool which the approving authorities have decided has a risk to benefit ratio which is not worth it. There things I have found airplanes will do, but probably shouldn't. I have written a number of flight manual supplements for modified planes in which I have restricted or prohibited certain things, because they lacked a suitable margin of safety, and just were not necessary. Often, this was based upon my having done it. An example of this, was that during my flight testing of a C 182Q, which was now equipped with a STOL kit, wing extensions, amphibious floats, and a gross weight increase, among a number of other mods. During testing, I let it get too slow on final approach (like 65 KIAS) power off. I got that really unsettling feeling, added power and sped it up. I then flew a number of intentional power off approaches to establish a suitable glide speed, and settled on 80 KIAS. This is an increase from the 70 KIAS for the original configuration. That speed left a margin for error and average pilot skill. I had to train the new owner in it, and with that glide speed, training went fine.
For myself, I find that if there is to be a judgement error during a forced landing, I'd rather see it to be fast/high than slow/low. As the original video shows us, you're better to go off the end at low speed, than crash short (and maybe out of control) at flight speed. My third forced landing (an EFATO) had me a little fast and high - surprise factor, delayed proper action. I came to a stop in the adjoining field about ten feet from the far end fence with full flaps, nose up elevator and brakes applied. No damage, not my proudest airmanship, but better than tangled in the trees at the approach end - and, should it have not worked out, I could state to the insurance company that I had done exactly what the POH and my training had said to do.