In all the terminator movies/ tv shows, they say that inorganic things can't be transported through time...?

Then how come all the terminators are able to be transported back to kill/help John Connor and his mother? They are made out of inorganic compounds inside, covered with organic skin. If they are able to transport back/forward in time, then can't they, by the same method (like covering up metal with skin), transport weapons back in time?