The origin of this is the fact comes from gameplay reasons, yes. If you look at PTRS in CoH 2 for example, the guards pretty much suck throughout the game. As we don't want to add abilities like "mark target" and stuff like that the idea is that ptrs/ptrds deal comparably high deflection damage to tanks, to make them useful throughout the game.
Of course, the amount of deflection damage can be tweaked if it's too high, but so far I didn't find it to be too high.
Also, a historical reference: because soviets couldn't damage heavy tanks by penetrating their armour, often all soviet units were ordered to focus fire the powerful axis heavies, destroying secondary weapons, scopes and other mechanical stuff which was needed to operate the tank. So, the tank was intact but was inoperable because the crew was "blind".