Pete, sorry, but you are technically incorrect. As Mike H pointed out, the hi-vel 9mm bullets in question probably do have more kinetic energy than the .45 bullets in question - not by much, but a little - all assuming the 210 loads are not atypical velocities. There is an indisputable formula to calculate this (E=grains*(vel^2/450000), I believe. For example, if the +P 115 grainers are traveling at 1200 fps, that's energy of 368 ft-lbs; whereas a 210 grainer traveling 850fps results in energy of 337 ft.-lbs. Power or momentum is another formula entirely, which would show the 45 with the advantage over the 9mm).
So, the answer must indeed lie in the amount of that energy actually transferred, due to ricochet effect, etc. If the 210 gr .45s are lead, they are softer and therefore "smush" more on impact, thereby transferring much more energy before ricocheting, relative to the harder jacketed bullets.