I fully agree that it's the showmanship that makes him great. He Also makes people believe that anyone could do it if they would train the 'skills' that he has, suggesting the skills he uses are mainly psychological.
Last week I was talking to a british girl who likes Derren "because he's not really just a magician, it's that i love how he's mastered these human skills we should all learn". His showmanship makes people believe that certain psychologic skills are possible and he has perfected them.
But yes, it's because of his showmanship