Woz says the limits on compatibility were intentional. I can't say; wasn't there. Wendel Sander was a "real" engineer with a PHD in computer science, so his design for the /// might have simply reflected his idea of a proper computer. The Apple II was (as has been mentioned) quite unusual for the day, and the A/// used the same slots and disk drives as its predecessor, so it was a bit of a mongrel. Not as conventional as IBM's Apple II copy (the original PC), but not as brilliantly minimal as Woz's baby. I was tempted by the Apple/// Plus and its super hi-res interlaced video, but during the short time it was made, I was too broke.
I have a couple of IIGSes in the closet, and some day I'll set them up and see what they can do. Assuming I find some more tuits, that is. Getting a round tuit here is near impossible.