The difference to me is that a bomber's primary purpose is to attack and destroy ground targets. The kills it gets are generally defensive and secondary to their primary function of destroying those ground objects.We don't get the same damage message from fighters, because their primary purpose is to kill each other.With the possilbe exception of the Sdkfz 251 with the rockets, the GVs to me are more like the fighters than the bombers. This game's roots are the air game. The AA vehicles are their to kill the aircraft. The tanks are there to kill the AA vehicles and each other. The fact they can be very effective at taking down ground objects is secondary to their role, not the other way around as it is with the bombers.
