Rigger,
Believe you're absolutely right with that: "It kind of 'evolved' " over time info.
Though, and as for me, such first became Really noticeable about year preceeding that first 3 day Iraq War. All military (combat troops or not) travelling or anywhere in public stateside then were usually dressed in fatigues.
Such seemed & still seems truly weird to me.
Way-back-when if we scouts were caught off base at either Kitzingen or Bamberg, West Germany with even with our snappy & starched tailored fatigues with spit-shined Corcorans or strap & buckle Cavalry boots (also known as Tanker boots),...we all would no doubt have been picked up by class-A wearing MP's, for being out of uniform
Damn! Add a yellow scarf to our fatigues or work clothes for some parade or inspection by Division,...and all must admit that we were some sharp mothers!!!
Whatever, nowadays even MP's in town stateside will most likely be wearing baggy camos, just like most clerk typists & such also do.
Dress-wise these days it's actually hard telling difference between combat troops, clerks & brig or stockade prisoners,...except for some having that big P on their backs.
Neil