Greybeard, respectfully, are you suggesting that the spec of the C-17 is less robust than civil airliner?
It's partly spec, and partly experience. By the time the KC-10A were built, there were DC-10s with already a dozen years in service. Civil planes get up to ten times the flight hours per year compared to military. Specs are built up from experience, of course.
There were several lightning caused failures and subsequent improvements made to the DC-10 before the first KC-10A was built, for example.
GB