It's actually both, specifically because of that incident. (Pretty much any time a commercial jetliner crashes, a rule changes, and it's been that way for decad

It's actually both, specifically because of that incident. (Pretty much any time a commercial jetliner crashes, a rule changes, and it's been that way for decades.) There's an hour number and a cycle number for many maintenances, and whichever comes first triggers the maintenance. Hulls, however are rated for a max number of cycles due to fatigue caused by the pressurization/depressurization and that's the part of the plane that cannot be replaced. So the plane usually gets junked or shipped to a developing world airline due to cycles.