I know that Matt summed it up (perfectly as normal) but there's another thing to think of.

USAKilts was formed to supply AFFORDABLE kilts to the public that didn't look like they were affordable. The only kilt options at the time the company was started were VERY un-natural looking kilts (you know the ones), too expensive for the normal guy, or were just starting-up and not widely known. USAKilts came-up with options in designs that would allow the wearer to look good and have money to spend at the Irish and Scottish shops at the festivals. Materials included the cotton-blends and wools that were readily available at a great production cost. Simple notion that helped to make it a FAST growing company.

The tartan kilts today have a few more vendors that are working with that philosophy. The Stillwater Kilts "Standard" kilts are a PERFECT example. The many styles of BearKilts are available and popular. These were designed to allow the wearer to go to the Festivals, Pubs, Games, Concerts, or whatever and not worry about the kilt. Those that TRULY know and appreciate kilts will know that authentic Traditionals are monetarily out-of-rach for most people.

"Walk with pride, Laddie."