There was an effort in the not-so-distant past to create Combat Armorcrewman and Combat Artilleryman Badges. The idea was quickly killed, as it is everytime some General with an Armor or Artillery background brings up the idea. The reasoning for the CIB is that in the past, Infantrymen have borne the brunt of combat operations, with little reward and lots of opportunities to be killed or maimed, while other branches don't (except for medics, who earn the CFMB). The CIB was created to recognize those sacrifices the average Infantryman makes in combat. Of course, as we've seen in Iraq, even supply troops are out on patrols and doing basic Infantry tasks on a regular basis. I wouldn't look for a Combat Supply Clerks Badge anytime soon though. IIRC, one reason for given for not creating any other combat badges was that the floodgates would be opened and every swinging dick would want one made for their MOS.
Those badges were created to sell to DATs and RedLegs who want something to show their service. As a RedLeg combat vet, I can say you'll never see me wear one.
As an aside, I do feel that some troops outside of the 11 and 18 series should deserve to be awarded CIB's, especially FO's. Forward Observers are right there with that Infantry platoon, taking the same fire they are, doing the same movements to contact, and sleeping in the same hasty fighting positions. However, since they are 13F and not 11B's, they don't get an EIB. Of course, as I stated above, if Fister's were awarded them, every 92Y that manned a traffic control point in Mosul would want one too.