To me it was reading about all the other characters acknowledging the horrors that had happened as such that made the whole thing feel more disturbing because of how real it felt. I remember reading Hyperion side to side with A Clash of Kings, and surprisingly finding the latter less disturbing even if it's hands down filled with way more violence. Now I realize it's because of how almost 'usual' the violence in that story (and, in particular, the world the story takes place in) is, so much that at a certain points the shock value of certain scenes fell completely flat.

The author of Kavalier and Clay has a nicely sized bibliography, so I wouldn't be surprised he was on a deadline and just had to get the book done in time, regardless of anything else.