It is important to have protection of helmets for the back of the neck when you are running away from a sword. Since we don't use swords, and we don't spend much time running away, the need for neck protection is minimal.

Just kidding.

But the improvements to our body armor and helmets seems to have cut down our death rate pretty substantially. The flack jackets that we wore in Vietnam would not stop an AK-47 round. The protection equipment worn now does stop AK bullets. Big improvement