Roberts clerked for Rehnquist back when he was still an Associate Justice, so he doesn't necessarily know how Rehnquist ran the court as CJ (except from the perspective of being a friend of his).
I'd bet Roberts learned more than you are giving him credit for. Management styles are consistent and learning them is long lasting and becomes inherent to the person taught. Add in, Roberts remained friends with Rehnquist since his clerkship and it would not surprise me that Roberts would run things pretty much the same way Rehnquist did. Of course, there's no way I can prove that, and it would be interesting to hear from some people who have worked for Roberts to get their take on it.