With the small amount of customization available for aesthetics, I believe that job outfits should be capable of being sold/traded. As it stands, they offer nothing other than looks, so why lock it to classes? The only reason I can think of is “for PvP”, but then again, why not just offer an alternate way to tell what your opponent’s job is?
Some may not even know what job you are after looking at your clothes either (since others [like me] may prefer the first job outfit to the additional ones you get later on).
Just food for thought.