Responding to Nick's comment about the A-1 in 'Nam, I recall some of us talking to a Spad driver at the time and he told us that on one occasion he was acting as a forward air controller for some fast movers, and he marked the target for their MK82 500 lb bombs with a couple of 1000 lb bombs.
On the other hand...
Same guy showed us a picture of a returned A-1 with the pilot standing in the hole in the wing caused by a 75 mm AA shell. The A-10 design philosophy clearly follows the trail of the A-1.
And yet, the A-10 loses favor because it is "slow". Although it can take a lot of punishment, speed really helps survivability. I remember looking at an operations research study that demonstrated that vulnerability decreases at the cube of the speed.
Apaches are effective weapons in a permissive environment, but unless you can really take advantage of terrain masking, at helicopter speed you are vulnerable even with a decent self defense suite.
An unnamed senior ex-military pilot. now with Sikorsky, once told an audience I was part of that an RWR is only good for telling you when to bend over and kiss goodbye.