The war in Iraq is different in that more of the troops there are under fire, than in previous wars. In the last century, as the number of support troops grew enormously, only 10-25 percent troops ever experienced any combat. During World War II, surveys indicated fifteen percent of the troops were in intense combat, while another ten percent were under fire (often shelling) at some time during their military service. This went down during the Korean war, up during Vietnam (where bases were often mortared or attacked by enemy commandos), and down again during the first Gulf War. But in Iraq, some 80 percent of troops have been exposed to combat. Often it's nothing more than being near an exploding roadside bomb. But this alone has caused over 50,000 cases of serious hearing loss. This type of injury often isn't even counted as an injury, usually because it's temporary, and the troops are used to loud noises in the military. Because of all the explosions and equipment noises troops encounter in training, the average soldier losses six percent of their hearing during a four year enlistment. This is above average for young people in good health, and no one but a medical researcher really notices it. Gradual hearing loss over a lifetime is normal, but the loss is accelerated by being in a job with lots of loud noises (some musicians and construction workers, for example, or a kid with a loud iPod). The military has always been considered a, "job with loud noises."
Exposing so many troops to combat has other consequences. Over the last century, most people joining the military have come to expect not being exposed to combat at all. As a result, they are not psychologically prepared for the stress. That leads to more stress disorders for non-combat troops who find themselves getting shot at, or exposed to enemy shells and bombs. Another liability is that combat troops (about ten percent of the army) are selected and trained to deal with the stress of combat. The rest of the troops are now getting more preparation, but they are still, on average, more shaken by the experience than guys who volunteer for the infantry.