If you forgive my injecture... But as I see it, it's like a business suit. Worn traditionally as a white collar business attire.. Over time the suit has changed, but it remains basically a suit. You have a single breast or a double breast, both traditional in the sense, yet different. You find suits on the market today, where they have a modern touch to them, and they may not be appropriate to the traditional business attire, but yet, it is a suit. There are no set rules written down, how one wears a suit, but there is a traditionally accepted style. One can wear it dressed up or down.
Suits are worn by peoples of all classes, and to their position/ or wealth is evident in the manner of uhh quality/ accessories. My mother talks about my grandfather going to the tailor to get his suits made, he was a blue collar man, so he would not dress as those of a white collar status, yet he wore a suit in the traditional manner.

The kilt is exactly the same thing, as Jock has pointed out, numerous times, it's an attire, to be worn as the situation dictates, by the blue collar, and white collar crowds alike. It has changed a bit over the years, but it's manner of dress is somewhat timeless.

My opinion, but that is how I see it.