When the Second Law says "indistinguishable", it means indistinguishable -- functionally identical in all important respects.
Alan Moore's Watchmen is a superhero story of unparalleled excellence.
It is also pure, unadulterated fanfic, in all but a single respect -- and that respect is that Moore recieved a paycheck from the corporate entity (a legal fiction of no literary relevance) that the copyright (another legal fiction of no literary relevance) to the characters upon whom the graphic novel was based.
EDIT: Thinking about it, with the possible exception of V for Vendetta, all of Moore's major works are fanfic.