I think you’re being hung up on the literal meaning of the words a little bit. It seems reasonable to have more severe consequences for someone attacking someone else with a rock compared to somebody just using their fists. We decided to call the former “assault with a deadly weapon”. This doesn’t mean that a rock is a “deadly weapon” under all circumstances. You can’t get charged with “possession of a deadly weapon” for simply walking around with a rock without intent of hurting anyone.