Just because Norton said Johnnycake's quote doesen't means he is Johnnycake
You may be confusing that a character is based of,and a character that has small features that remark another character: Norton looks completely different to Johnny Cade,and he doesen't shares his personality much at all...But he says that quote in order to make a reference to The Outsiders,more specifically,Johnnycake..
But yeah,at that point you're right,there're characters that resemble other ones...Y'know,Ricky resembles Claude Speed (GTA III main character) quite a lot...But,the difference might be that Ricky can actually talk