The big reason for less wear, the LEAD was taken out of gas. You oldtimers remember how bad the plugs looked after 15,000 miles. Today they go 100,000. The lead ate up cylinder walls and exhaust pipes in no time, very corrosive.
Unfortunately I can't agree with anything you say in this post. They took lead out of gas, because it was accumulating along road ways, and causing health issues. Plug electrodes used to be made of steel, now they are made of platinum to meet emission requirements for longevity. The byproducts of combustion can be very corrosive, but it is the condensation(H2O) that used to mix with sulfur(sulfuric acid) that could cause premature exhaust failure, especially with short trips. Exhaust pipes are now made of stainless steel. Better fuel management, better oil filters, moly rings and other standard improvements have minimized internal wear. Don't get me started on cheap oil and cheapskates who won't do normal maintenance.
