I think Dave got the French cuff shirts, not for a sense of style, but as a functional part of his job. When stressed out, it’s very easy to chew off buttons. However, metal cufflinks are much harder to chew through and you can still look good after wanting to throttle an employee or having a bad day. It also illuminates the fact of Dave having to bring scotch, and or any other type of tranquilizers to work.