For a WWII pilot, it would be a lot easier for a fighter to tell if a plane is down or not. It's not as easy for a bomber to count buildings, or determine if the building is destroyed, what qualifies as destroyed? Fighters could quantify enemy planes really easy, if the plane went down... one. It was impossible to quantify damage.
But in this virtual world we love so much, we can quantify it easy, so why not take advantage of it? Fighters get plenty of benefits from the virtual world. Off the top of my head think if you shot someone up and they head home. You'd never know what happened to that pilot and cannot confirm that as a kill. What if that guy crashed as a result of the damage you had done to him, well through the magic of AH he could be hundreds of miles away yet you still get credited with a kill.