It's interesting that when Batman was introduced it was at a time when comics were just starting to get off the ground and seen as entertainment mostly for kids. And yet the Batman of 1939 carried a gun and actually killed people during his exploits. He really was grim and dark and yet intended for children's entertainment.
Comics were an offshoot of the pulp magazines and the stories tended to deal with content painted in broad strokes without much subtlety and nuance. It was easy to grasp and the (relative) simplicity could even appeal to adults well familiar with the varying shades of grey of the real world. In some ways that remains part of why superheroes still appeal to us---they are the good guys getting the job done while everyone else seems to be just talking things over and arguing without result.
After reading this book I rewatched Batman Begins
and The Dark Knight.
While Nolan certainly makes an admirably effort to put Batman in a more realistic setting the pulp/comic book original source material is still very evident. As realistic as Nolan tries to be he never fully gets away from exaggerated and over-the-top elements. That's not a bad thing, but you can't help but see it. It's an acknowledgement that this is indeed fiction and still uses occasional broad strokes to heighten the drama.
Ironic, though, that Nolan's Batman of 2012 can't bring himself to directly kill Ras al Ghul or the Joker or Bane or anyone else, but the Batman of 1939 likely wouldn't have had that inhibition.