Read Trust Me: Four Steps to Authenticity and Charisma by Nick Morgan. It's a really good book, and touches upon that point very nicely. It might seem paradoxical, but EVERYONE who's in the spotlight is trained to act "genuine and charismatic." Some people learn faster than others, but in the end, before you do something like host SNL, you will have received a lot of coaching.
Oh c'mon; if he had received training, people would have chided him as being faked and rehearsed. He's damned, regardless of what he does.