when i refer to body method or "shen fa" if ya want to speak some fancy chinese. i am talking about a method that is specific to the art you are developing. for example a hsing i punch has a different set of standards and method than a tai chi chuan punch.
in self defense it does not matter as long as you keep you and yours safe but in practice and in teaching i think it is important to be clear about what makes each of these styles special and worth your effort and to also keep them seperate until you have enough personal understanding to mix them as you please, at that point it is your art.
you are right the human body is very tough. it can take a lot of damage and keep on going (although sometimes people just drop from the "right" punch.)
in many cases martial artists who have never been in a self defense situation have a false sense of security about what they may be able to do.