the whole psychology and habit around closing is just that, psychology and habit. Jim Leyland showed us in '06 that using your best reliever when the leverage was highest should be the way to go, but the habits formed in baseball culture, which includes the fans, the press, management and even the players, all pressure teams to have closers. It make very little actual sense statistically or tactically. Even the argument that the 9th is somehow harder to pitch is only true because players have come to believe it.