Well, here's one example.
The stress in a highly heated part of the rotated machinery in a gas turbine is highly dependent on the temperature of operation, especially the peak temperature. Such that a change in operating temperature of only a few tens of degrees can commonly double or half the effective fatigue life of the component.
the parts are not manufactured to different standards; they are USED to different standards.
Military fast jets are not manufactured to lower standards than civil airliners. yet hardly any military aircraft manufactured in the 70s is fit for continued operation without substantial rework - think of all the rewinging programmes the military routinely conducts to extend the service life of older aircraft. When was the last time you heard of a civil aircraft being re-winged? They dont need to it, because they are "babied" compared to their military brethren - one aircraft flies at a sedate 0.8'g' to 1.5'g', the other between -1'g' and +6'g' perhaps.