I think a lot of it has to do with the ignition system that the car has in it. Years, years ago I had a '94 LeSabre that I installed BOSCH +4 plugs in. I was a young kid and thought I was doing Good to an old relic putting some fancy German plugs in.
Car ran like garbage after a few weeks. Put new Regular ACDelco plugs in it and it ran great again. In doing some research, I came to the conclusion that the LeSabre of said vintage had an ignition system where it fires a waste spark opposite of the ignition. So essence the plugs were doing double duty.
Perhaps manufacturers of plugs, in particular applications, account for these set-forth endurance requirements.
As far as I have always known, NGK makes ACDelco and Autolite makes Motorcraft. As a universal plug, I have always used NGK in everything with no drama. Many of my Honda's have come OE with Denso. I have replaced factory Denso in Hondas with Denso again and with NGK and both performed just as good.