If the wing of your 747 falls off and they find out a part is at fault, they can quickly locate all the planes that have parts from the same batch.
I suspect the Mil Spec system grew out of the military desire for orderly sameness, the ability to get the same thing from numerous suppliers, and be assured "the lowest bidder" isn't cutting corners. But of course, like anything the gumint does, it grew like topsy.
It's like "Mothers against drunk drivers", if you criticize any aspect of their dogma, you're labeled a heretic that doesn't support the troops.
The military is getting savy to the fact that by going through the lengthy process they won't get the latest and greatest. This has become an issue as they rely on more high tech materials and electronics. Some military aircraft are going with electronics used in commercial planes. That is for non-weapons systems of course.
