Well, you COULD implement that, but it would really be a bitch for developers to have to make certain walls smash-able and then place smashable walls, etc. and have to use up more RAM with space being used for smashable\unsmashable copies of the same wall. Fallout is fine without wall-smashing, and although driving over people would probably be easy enough to do if you configured the radiators of vehicles to act like lines of mobile grenade explosions---that would still take up RAM. We don't need this kind of stuff, I'd personally like more types of NPC models, animations, and gun appearances than the ability to knock over walls.