i had a 74 power wagon with that type of coupler, [it's been gone since '83] and i thought it was an extra measure to insure the shaft didn't bind during any added flex when the cab and frame moved around during off road excursions ? i never had one of those apart however, to see what was inside. if you have a rag joint, the "common" type of coupler, and the one you show in your last pic, it should add quite a bit of movement before the steering shaft would bind up. does anyone happen to have a shot of the insides of one of those joints ?

upon more reflection, that coupler might allow movement in and out to a certain degree ?