Gen I cars did not have an airbag, so the Federal Government mandates that the seat belts when not equipped with an airbag are passive. That means they work without having the operator have to latch them. If you keep the belt latched, you can open the door, slide in and close the door with out the belt having to be buckled. Therefore it had to be on the door. Canada did not have this law and that is why the seat belts are in the center like Gen II. Gen II cars have an airbag, therefore its easier to package in the center (structure wise of not having to reinforce the doors) and its common in all applications, so they were located in the center. Gen III cars have airbags, so they could be packaged in either location, Chrysler choose to package them closer to the door as the structure is more ridge and easier to control. So that is the reason, not for athestics but to meet seat belt standards and performance requirements in an accident.