Sampling is not just cutting a fragment from a song and calling it a day. Usually (if you look at Prodigy's tracks for example) it includes transformation so that the result doesn't sound much like the original. For example, you can sample a single note and make a melody from it. Or turn a soft violin note into a monster's roar.

As for DJ'ing I would say it is pretty limited form of art and it requires lot of skill to create something new this way.