My impression is that "plays pretty well off Drew" was, far and away, the most important criterion, much more so than the sound of his voice or how well he reads copy. I'd further guess that his good-natured sportsmanship during the April Fools episode went a long way toward cementing the offer.
Once again, purists probably will be up in arms, but frankly, I don't understand why they're even watching the show anymore.