This rule is the reason i like blasterborn in venoms.
troops in back can shoot a transport - destroy it.
the venom then can unlesh the duel splinter cannons into the unit as they disembark from the wreckage.
however if you do not explode the vehicle MOST players will put to transported units BEHIND the wreckage out of LOS.
Those who live by the Sword, get shot by those who don't!