This is why the President nominated him, because he had spoken with him many times and talked to those who have known him for a long time.
Especially people like Ted Olson who has tried cases with and against John Roberts and has known him personally for 25 years.
One thought I had listening to Roberts and his answers is, "Can this man possibly be a persuasive force with the other justices who vote liberal?" In other words, can this man by more than his single vote on the bench, exert enough influence and persuasiveness that will move the other more liberal justices? Thomas and Scalia I am not worried about.