Mil-Spec is a term often misunderstood. The specifications in a military contract have to meet those standards. Are they the best made part? Not necessarily, they just have to conform to the standards of the specifications. Does every part have to be tested? Only if the contract states it does.
Look at the Ford F-150 commercials from 2-3 years ago. The aluminum is military grade. What the heck does that mean? How many different type grades of aluminum does the military use? I'm sure dozens.
Civilian AR's are no different. Colt will say mil-spec, and I'm sure they do meet the same standards from the military contract. Doesn't always mean better.