Djing?

There is one thing that i have tried to pay attention to and is the art and science of djing. What are the rules of good djing then. I have started from the basic principle; you have two decks and you are going to select songs and fade one into the other as smoothly as possible. For more advanced djing matching the keys of the songs or mixing in keys using effects filtering, adjusting bass and treble etc. But recently i have started to question this method as standard and contextual as what i have been seeing  interms of djing is the opposite (I have not seen club djs yet, but i anticipate they don’t leave spaces in the music). I am now a bit confused; is it djing is differet from selecting is there something i missed in there, do different styles of music require different treatment. Instead of two turntables i have seen one. you select one song play it out and then start another so there is a pause in the music which i have always thought was not suppose to happen. The crwod doesn’t seem to mind but i am trying to understand what makes this idea work and how does it compare to the way i have always thought one should dj or least learnt it should be done.
There is one thing that replaces the fading of one song into the other and that is talking in between songs and dat is for the more entertaining djs. So I begin to notice and reconsider styles, audiences and history of the dj.