The difference would definately be the amount of room between the axle and the frame, trucks tend to ride higher, so to make the shocks reach they are mounted in a verticle alignment. in a car the axle is much closer to the frame, so they would either have to use expensive specially designed short shocks or mount them at an angle so that you get decent shock travel with little axle movement.

one thing to ALWAYS remember about cars, the cheaper easyer way always makes it to production.