You don't have to bring all of the other wiring of a house up to current code when you're doing a service change, why would you have to bring it up to current code simply because you were moving an outlet over? Other than putting in a GFCI receptacle.
When do you have to? If one was changing out a main panel would he have to make sure the rest of the house (e.g. bathroom 20A) was up to code?