GM had a lot of cars (All J, N, and A body cars, to name a few) with door mounted seatbelts, as it was a cheap way to get around passive-restraint system laws mandated by NHTSA. The idea was to leave the seatbelts buckled at all times - opening the door would stretch the belts away from the occupant enough to be able to get out. Bingo, no need for an expensive airbag or expensive motorized mousebelts. Of course, the reality is that people would end up looking like a bug caught in a spiderweb when used as intended, and everyone just unbuckled the belt like a normal human being when they wanted to exit the car.

While the pivoting holder on later model SVXs is nice, as well as Mercedes' motorized valet arm, the trick solution is what is found, ironically enough, in a lot of GM vehicles these days - seatbelts mounted to the seats. The Mercedes SL first used this concept, but GM has adopted it as it's own, using it in Cadillacs, their full size trucks, and others. It allows for better adjustability and fit, easier ingress and egress into the back seats, and are generally shown to be safer as well.