I drive a mail truck, and some of the new prototype designs have mirrors out like that bus. The problem on the current mail truck is the mirror either blocks side visibility at an intersection, or slams you in the shoulder when you get in and out. I'd say that bus is done to improve side visibility especially at say a 4 way stop. It may have also then shown to improve aero, but I know first hand classic mirror placement kills visibility
here is a picture of what would be the blind spot out front with cross traffic. Imagine standing a little forward of where this picture was taken and the mirror fill the window meant for 1/4 ahead visibility.
