I haven't seen the show with Drew, but it would seem that he lacks the sincerity that Bob was at least able to fake. Yes, I meant that. He really did come across as though he genuinely cared about the participants. I doubt he did, and imagine his would be a hard act to follow for anyone who has become a tried and tested Hollywood talent (and therefore a gazillionaire as well). At some point, I don't think most of them can identify with the everyday Joe's of the world. Of course, Bob isn't the only one who can fake this. Take Oprah, for instance! Please, take Oprah!
While Drew has the wit and spark, I also suspect that as a natural comedian he'll want too much of the attention to be centered on himself. Bob was good at taking center stage at the right moments, but then sharing it with the contestants when it wasn't all about him (i.e., once the game gets underway). But we'll see. Maybe he'll find a way to pull it off and give a fresh perspective to the show after all of these years.