I don't know if you guys have ever actually worked with MIL-SPECS, but they aren't any more stringent then most commercial specs. In fact, many MIL-SPECS has been superseded by commercial specs.
As far as "Every part is milled to a specific spec", all machined parts are milled to a specification (called tolerances). MIL-SPECS aren't necessarily a tighter spec as tighter specs can lead to less reliability.
Colt manufactured to a mil-spec in some components since those components were shared with the firearms sold to the military.
I was in the military for about a decade...worked in more then one DoD supplier (mostly QA in machine shops). MIL-SPECS aren't some holy grail...they're just specs.
Now, when NASA was involved, different story..and after the USS Thresher incident (in 1962), zero defects in submarine building meant zero-defects....but all in all, MIL-SPECS weren't really that stringent.
But, use of the term "MIL-SPEC" in advertising sure sold some Colt AR-15 rifles!