If you try to research the Pentagon-level reasoning behind most land-battlefield military weapons, in particular small arms and personal weapons, you'll find that they are intended not to create FATALITIES per se, but debilitating/incapacitating CASUALTIES(i.e. wounding rather than killing). There are a couple of reasons behind this.
The public-relations rationale usually invokes the Geneva Convention/Hague Accords, which assert the basic premise that a uniformed enemy soldier is a basically honorable person who is serving his country just as you are serving yours, and the humane thing to do in combat is not necessarily to kill him outright with something like a dum-dum bullet or poison gas, but to incapacitate him with a wound that removes him from combat yet allows him to recover and return to civilian life after the end of the war. Yes, this does reflect the thinking of a bygone era, and is very difficult to rationalize in an age of racial/ethnic genocide, irrationally fanatical terrorists and weapons of mass destruction.
The other rationale comes from Von Clausewitz' writings and is more strategic in nature, in that an enemy soldier who is killed outright is less of a drain on his army's/country's resources than if he is merely wounded. As Boondock Saint noted, a wounded soldier also takes his buddy out of the fight, provided that his buddy is willing/able to drag him off the front line and patch him up(not something usually seen in Japanese banzai charges, Chinese "human-wave" attacks, or mujaheddin skirmishes). Theoretically, a wounded soldier also drains medical supplies, rations, money and other resources from the enemy nation until he either recovers and returns to duty, or dies. By contrast, if an enemy soldier simply dies outright, all that happens is that his buddies have to dig a grave for him, his CO has to write a letter to his mom afterwards, and the unit drives on and continues its mission. Again, this tends to be more applicable to "civilized warfare" as opposed to current conflicts involving enemies with less concern for their wounded personnel than we would consider normal.
As far as the weapons/cartridges of the past, they were still intended to accomplish the goal of creating casualties, not fatalities - at the turn of the century(.30-06), military thinking held that you had to be able to do this at ranges of 1000+yds(witness the Boer War), therefore your rifle and its ammo had to be sufficiently powerful for the task, and the greater lethality at close range was just a nice thing to have when the enemy got uncomfortably close. (BTW, during the Spanish-American War, the Filipino juramentados weren't particularly impressed with either our .30-40 Krag service rifles or our military ethics, and usually had to be killed outright at close range with shotguns or .45's - you'da thought we'da learnt better after that...)
During/after WWII, we still thought we needed a rifle and cartridge that was capable of accurately hitting and incapacitating an enemy soldier out to 600-800yds, hence the M14, the FAL, the G3 and the 7.62X51 cartridge. After studies that indicated that most infantrymen simply didn't bother to shoot at enemy soldiers farther than 300-400yds away, the Pentagon planners decided to sacrifice the long-range performance of the .30-06 for (marginal) savings in weight/material cost realized with the .308/7.62X51 cartridge - yet they just couldn't bear to completely give up the .30-06's effectiveness at medium ranges.
Given the short-range nature of jungle warfare in Vietnam, the Pentagon planners thought that the M16/5.56X45 would still incapacitate(if not kill) enemy soldiers within short ranges while affording the triple advantages of a lighter weapon, with less recoil, and lighter-weight ammo, which allowed the soldier to carry more ammo/gear, which would allow him to shoot more, or shoot full-auto more accurately, which required him to carry even more ammo...ahem. As originally developed, the rifle and its ammo actually performed pretty well, although later problems would arise with the ammo and with the rifle's maintenance(but that's a whole 'nother can of worms). Vietnam was where the first reports of explosive bullet fragmentation and ricocheting inside the body came about.
In the later years of the Cold War, the Pentagon planners decided that the 5.56 cartridge needed to penetrate light cover or Soviet helmets/body armor at longer ranges in order to successfully create enemy casualties, so they optimized the rifle and cartridge to fire the 62gr. steel-cored armor-piercing SS109 bullet. In doing so, they caused the rifle/cartridge to lose much of its effectiveness in return for the capability of causing at least a minor wound on an enemy soldier whose armor or equipment would have deflected the previous 55gr. M855 bullet. The M16A2 rifle with its SS109 ammo subsequently became infamous in the Somalia action(q.v. Blackhawk Down) for causing non-dynamic, non-explosive, ineffectual through-and-through wounds on un-armored(possibly drug-fortified) Somalis who would have to be shot 5-6 times before finally collapsing or being incapacitated.
So, basically, while the end result(enemy casualties) is the same in the Pentagon planners' Big Picture, the grunts with mud on their boots tend to STRONGLY prefer that those enemy soldiers who are shooting at them become Dead Right There, As Soon As Possible; while 30 seconds or 5 minutes may not change the overall result of a battle, it can and does make a difference to an individual infantryman if the guy he shot is still able to throw a grenade or empty his rifle on full-auto before succumbing to his wound...
traversing through the gutsack, exiting in front of the haunch, entering the haunch, traversing down the back leg, exiting at the knee, and entered the hoof and exited to God knows where. Certainly nothing to count on.
