If you knew what Colt/FN actually asked for their M16s and M4s from the government you would probably realize that the extra few hundred they tack on for Joe Q. Public is a scam.
I've been around hundreds of ARs in usage. Add in my military service and that would go into the thousands. I've witnessed 3 mechanical failures in all that time. 1 military and 2 civilian. The civilian examples were 1 loose gas key, and 1 case of broken gas key bolts. The military failure was a loose hammer pin.