Looks like a matter of some increased attention to detail in certain areas, addition of "bolt on" modification (Jewell triggers, Ti firing pins?) and useless "all the rage" features like chromed bolt/carrier on the Les Baers, and RAS on the KAS.
I doubt that the custom made forged components (KAS, Les Baer) have any significant impact on accuracy, just adds to the brag factor.
I also own a Wilson Combat upper; nice AND competitively priced. I've handled the KAS, very nice, and good if you can get one for $1200 (price of average AR plus the RAS, 2-stage trigger and flip up rear sight). Since they're trying to sell them for $1600, I'll take a pre-ban Colt instead.
Basically, they're the high end for those who want a little higher level of finish and a name they won't see on other's AR at the range.