I don't know, but both Gemini and Wikipedia in my primary language seem to agree that AWD refers to 4WD with a center decoupling mechanism to run front and back in an asynchronous manner, with emphasis on Wikipedia only that this is strictly American definition of it and both describe both style of systems in the rest of the world.

I'm guessing that maybe a distinction between offroad capable cars and non-capable cars is useful for liability reasons. Or something else.