For what I pay for the OEM plugs, and the opportunity to wrench on my truck (albeit a PITA with the plugs at the firewall), and more importantly the experience for my little daughter to sit on the fender with her legs inside, getting greasy helping me out, is worth every penny!
I also don't disagree that the plugs can last longer and run well for longer durations, however, my peace of mind and a clean spark keeping my HEMI happy is worth it too. The parts industry makes money off me, yes, but I sleep well at night and know that I can hop in my vehicle and drive across country at a moments notice and have full confidence that I'll have zero issues.
Hell, I replace my serp belt, and the idler and tensioner pulleys too at 60,000KM's as part of my full tune up maintenance regimen. Plus a coolant flush and fill and a new OEM thermostat as well as a PCV valve. I clean my TB twice a year too!