BUT...the violence in TDK is tastefully done. As is the dialogue. There's really nothing that would earn it an R-rating. Deadpool on the other hand had gory violence, crass sexual humor, and expletive filled language. The language alone would nab Deadpool an R-rating.
From the categories the MPAA judges when handing out ratings, TDK doesn't even come close to an R-rating. It has nothing to do with Nolan pulling strings. It just rides the line. There is no blood, no foul language, and no sex or drugs. The only scene they might've looked at a bit, is the phone bomb scene, where they show the after surgery with the phone in the guy's belly. That was real close to something they might deem a bit too disturbing and grotesque for PG-13. The hanging scene might be up there too. On the whole though, it's a fairly typical PG-13 cut.