You are right that scope of DPM practice varies widely (no two states are even exactly alike). I believe a unified national scope of practice is needed and will bring more credibility to the profession and understanding of DPMs; that unified scope is an APMA and ACFAS goal right now.
Presently, I know Florida and Georgia are APMA "model states" (means they are states with a great DPM scope). I think Michigan, the home of the first pod residencies, is very likely to be another "model state."
I am fairly sure that South Carolina, NY, Minn, and some other states have a pretty limited scope of practice (essentially forefoot only).
More info:
http://www.podiatryonline.com/main.cfm?pg=pro_development&fn=scopeofpractice
This was actually our homework for 1st semester Intro to Pod class: we had to find out the scope of practice of our home state.