The ratio of dead to wounded in Iraq and Afghanistan is approaching one killed for every ten wounded. This is a dramatic increase from Vietnam, where it was one and five. That was itself an improvement from World War II, where it was one and four, and earlier wars where is was one and three. There was a reason for the higher survival rate in each war. During World War II, the introduction of antibiotics not only greatly reduced the deaths from infections, but allowed surgeons to attempt more daring procedures. The problem with surgery had always been the risk of infection, but antibiotics like penicillin, changed all that.
In Vietnam, the use of helicopters to reduced the time it took to get casualties to an operating room. Better surgical procedures and medicines helped as well. That's what has played a large part in the much higher survival rate currently. That, and more rapid and effective application of operations research (using stats, math and common sense to solve problems) to identify areas where more improvements can be made. Improvements are implemented rapidly, month by month (and sometimes day by day, since the Internet allows new ideas to get around a lot faster.) It's dozens of small changes that are making the difference now, and that continues.