He had all sorts of input into it, he may not have been there a lot while they were making the actual full length film, but some years before he worked on storyboarRAB, some characters(one Jack Skellington), the look and so on and Selick and his wonderful crew worked on it from there. It's out of Burton's head in the first place, that is for certain. There would be no Nightmare Before Christmas.
It's his original film concept, others built it up and worked on it. Nothing wrong with using his name to promote it for that reason alone and giving him credit for creating it in the first place.
I know what you mean though, the other guy did do a lot of stuff too with the important stuff of the actual stop motion that Burton couldn't be arsed to do.