My quick, very short comparison.
What is the same:
Individual Tanks and heavy weapons, squads of infantry.
Insane attention to detail.
What is different:
PE - Real time
CM - Turn based, Simultaneous turn resolution
PE - detailed terrain with individual trees
CM - more abstract terrain
PE - First Person (you are a platoon leader and can only give orders to platoon members)
CM - Third Person (Typical wargame role blurring, can give everybody orders)
PE - American vs German in Africa, Italy and France (1942-1944)
CM - Western Allies vs Germany in France, Germany
CM owes much to it's wargaming legacy and is the next great step forward in wargaming. PE is a "flight simulator" for tankers.
I have played wargames for years from "outside the map" and enjoy being able to jump into the turret with PE.