edpmedic - It's not that the Armalites don't get dirty, but your BM does.
It's that the carbon at the bottom of the carrier doesn't matter - you don't have to clean it at all. It's self limiting.
I used to work for HOURS getting ALL of that carbon out. My cousin, former USMC infantry showed me how they cleaned it out - with a piece of cleaning rod and a patch pushing down hard and going in a circular motion. Of course there is only patch at the bottom of the rod section for about two seconds as the rod eats through the patch quickly. I thought "oh no - this is like a cylinder bore on a car and should be treated gently". I figured out that the very back where the scraping is done, and the very front where the other contact point of the cleaning rod is will never be touched by the gas rings, so I didn't worry too much about it.
Then over a year ago, I read the Armalite article.
I have MULTIPLE CASES (at least two cases per rifle) through my guns now since I've stopped cleaning the back of the bolt carrier's bolt cylinder. No ill effects.
As for being anal about cleaning - you'll find nobody who cleans and oils there firearms more thoroughly than me. BUT I don't clean the back of the bolt carrier - it's a waste of time.