Re: Tdk vs Avengers
Comic books have a wide range of stories contained within. Nolan broke the ice, but really these movies branching out in tone was inevitable.
How many comic stories broke ground and pushed the medium to new horizons? Plenty: The Dark Knight Returns, Watchmen, Kraven's Last Hunt, etc. The potential is there in the source material, Nolan didn't invent it.
It was just a matter of time before somebody realized the vast opportunities these characters have for cinema and that they can be used to tell any number of stories. Once they took it seriously enough.