The incredibly low coalition casualties in Iraq were the result of several factors. The two major ones were new and improved body armor, and realistic combat training. 

The body armor innovation is the first truly rifle bullet proof vest. This is called the Interceptor Vest, and after the war is over and all of the vests used can be examined for hits, it will probably be discovered that many (perhaps over a hundred) deaths were prevented because the vest stopped a high speed rifle bullet. When a bullet hits a vest, the multiple layers of super strong Kevlar cloth, and the ceramic plates, are deformed in stopping the bullet. The soldier knows he is hit, as it feels something like getting hit in the body by a padded sledgehammer. It often knocks the wind out of the victim, sometimes cracks a rib and almost always leaves a bruise behind. But in combat, many troops recover quickly and get back into the fight. But for several days they will be nursing that bruise. In addition to giving protection, the vest also enables a soldier to act a little bolder without feeling suicidal. This gives well trained troops an edge, as they can move and position themselves more efficiently in combat. 

But this only works because of another advantage. For two decades, American infantry have been practicing firefight drills using a realistic method of simulating rifle and machine-gun fire. The military calls it MILES ((Multiple Integrated Laser Engagement System), but it's basically laser tag. Each rifle and machine-gun is equipped with a laser light device. When the soldier pulls the trigger, the gun still goes "bang" (blanks are used). But a coded laser light also goes downrange as well. If another soldier is in the way, his laser light detectors will sense the shooters laser and the soldier in question will hear a buzzer go off, indicating he is hit. The range of the lasers for rifles, machine-gun, anti-tank missiles and tank guns are all set realistically, as is the damage they cause. So a rifle can't take out a tank. This revolutionized infantry training, because now new troops quickly learned to take cover. Instructors who are combat veterans have always struggled to get this extremely important point across to their trainees. With MILES, the point was made quickly. The troops were young and competitive and didn't like getting "shot." They soon became very adept at moving around on the battlefield without giving the other guy a clear shot. As the Iraqis quickly discovered, this is a deadly advantage for the guy who has it. 

The Interceptor vests cost about $1700 each and weigh 16 pounds. The MILES systems, per soldier, are a lot cheaper. But the net effect is to reduce friendly casualties enormously. Most current infantry are unaware of how much this has changed the way American infantry fight. They take for grated the realistic MILES based infantry exercises, which have been around since the 1980s. The Interceptor vests were introduced in the 1990s.