Oh, that's a good explanation NJ. Sort of like Hannibal's tan lightweight jacket he always wore on the A-Team?
The only thing with that would be, I'd expect them to show some of the "jacket" below the belt a-la Recondo.
http://www.yojoe.com/action/84/84images/recondo.shtml
However, they didn't on Duke, so it always looked more like a shirt tucked-in, than a jacket....
Your idea has good logic behind it - it's just that if that IS in fact the reason, I would think Hasbro could have materialized that
better if
they did his outfit more like Recondo's jacket. Instead, they left me scratching my head.
Good reasoning though!