I had just made a comment about how, yes, the studio engineer could do a high pass at the console during a live session but then I had a thought. Perhaps they train everyone to use the HP switch so when they are doing recordings without an engineer that they still get the same sound...? IDK... To me it sounded more like a "policy" than a true part of their "sound". In other words... it's a training function that makes the engineer's job a little bit easier.