My hypothesis as to why North Korean rhetoric is so hyperbolic is based on Anil Dash's Law of Fail:
Once a web community has decided to dislike a person, topic, or idea, the conversation will shift from criticizing the idea to become a competition about who can be most scathing in their condemnation.
North Korea isn't a web community, but its media is an insular echo chamber. Add to that the fact that dissent - or even just not keep up the daily denouncing arms race - can have serious repercussions for someone and their family.
What I have heard seems to indicate most North Koreans know, on some level,that the rest of the world isn't the way their government portrays it, have only ever seen politics explained in us-vs.-everybody-else terms, and that frames what little actual information they get.