I agree a .45 is a great round but 'knock down' power is a bs play on words. History is often full of bull stink and this is a fine example. 'Fall down' would be much more applicable a term than knock down as the bullet puts into motion a number of things that causes a person to fall down, and it is the energy of the round actually knocking someone down. There have been a number of people who have shot themselves in the chest while wearing body armor, some of the shots coming from 45s and some from various other calibers. None of them were knocked down - none even fell down. What someone implies that the 45 caliber round conveys enough energy into the target (in this case an adult male human) to actually knock it down, I find it rather amusing, and when someone says that the energy of a round lifted a bad guy up and propeled him through the air, well I believe it quite farcical. On the other hand, I could strike you while you were wearing body armor, and I could conceivably knock you down, especially if I used a full body blow. Yet it is unlikely that my body or any part of it would penetrate your body cavity whether or not armor was being worn, just as it is unlikely that the force of my blow would lift you airborne and propel you through the air.
And yes energy is bled off but in both directions. The energy of recoil felt by the shooter is quite close to the amount of energy transferred by the bullet to the person being shot. Of course one of the big differences is that the person who is shot has tissue damage from penetration, and suffers shock due to that rapid tissue damage, blood loss, impact of the projectile and so forth. A 45 does that work much nicer as compared to a 9mm, but I will take what is at hand and hope for the all critical shot placement. Of course it is nicer to have a round with better penetration capabilities should the adversary be wearing body armor, but in that case even a 45 may fall short. Then again this is when shot placement comes to play, and as some would say: two to the chest one to the head....
By the way, a quick 8 shots to the chest cavity of someone wearing body armor, would probably hurt a bit more with the 45 than would a similar amount of shots from a nine, yet I wonder though which would be more likely to penetrate the modern body armor better.
As for repalcement of the 38, I believe the 38 was also replaced, in great part, because of the insufficient penetration properties of the round in the body armor worn by the warriors in the Philippines. Of course some may claim that the 45 is a one shot man stopper (heck I have even heard that if anyone is shot in the arm with a 45 he goes down immediately - LOL), but my guess would be they have a nasty surprise coming if they ever shoot someone once with a 45 and then assume the threat has ceased because they were shooting wonder bullets.
Rather shoot till the threatening adversary stops, then make sure the threat is truly over with, as you help assure your own safety behind any available cover. That way you are more like to enjoy a few :beer: while you tell your 'war story' at a later time.
All the best,
Glenn B