"One reason that comes to mind is the reliance on the Emperor Pantocrator either in Byzantium or Russia. The Orthodox Church -- except perhaps on its geographical periphery or at some historical fault lines -- had a cooperating state of which Gregory VII would not dream."
Until 1453 this was theoretically the case, though in fact it hadn't been really true for some centuries before that. After 1453 most of the Orthodox world was under Mohhammaden oppression. Russia is a different story of course. Your point is well taken though and it seems to me that the way Petrine Primacy developed in the West was a direct result of "facts on the ground" in the West. The task ahead of us all now is to come to an agreement on what that primacy really and practically can mean in a united Church today. Even the Orthodox accept that it is more than a mere primacy of honor .
Thank you for this post. I agree that the modern papacy developed at least in part in response to the ills of modernity, that also originated in the West. For example, the formalization of the doctrine of the Immaculate Conception is thought of as being due to the materialistic view on the nature of man. To them who deny the reality of theosis we say, look at Mary, the true woman.