The JTRS, called "jitters" for short, is a software defined radio protocol that includes voice comms, internet, data, etc. It is supposed to allow all new US military service radio gear to communicate with each other (ground, air, naval). A good idea, but much was asked for and it has been way over budget in some of the development programs. The deal with troops using FRS/GMRS is that US Army/Marine policy has never been to supply each marine or infantryman a personal radio. Each squad of 15 to 20 men would have a designated radio/operator to securely communicate with headquarters. Law enforcement issues each officer a handheld radio because they usually operate solo. The urban anti-terrorism operations in Iraq and Afghanistan tend to be more of a police type action with manhunts and door to door sweeps than with traditional combat defensive/offensive operations. As an ex-leo, you can see that it would be hard to do these without comms between individuals since by necessity some guys are going to be out of hand signal sight covering exits, etc. I am agree with you, FRS/GMRS radios would not be my first choice, but it appears that for quite a while, they were the only affordable answer and they did work. Commercial off the shelf radios such as the Icom F40GS with the encryption module and the Motorola XTS2500 digital radios are much better. The DOD was obviously not prepared for the occupation of Iraq at all. However, the main mission since 1945 was stopping the Red Army's offensive push into Germany and they were equipped for that mission.
Bob