My uncalled for 2c worth. It would seem that this debate is not an “either - or” matter. Diesels last longer for both the engineering aspects as well as (hopefully) the type of person that owns them. (Warning, redundancies forthcoming)

The engines are built ruggedly to survive the inherent stresses placed upon a diesel combustion process. The slower engine speeds are a factor as well – the rate of wear vs. RPM is a logarithmic relationship.

The owners are usually people that are relatively easier on their cars, not someone looking for 12-second quarter miles. They are not going to beat the hell out of an engine, they are more likely to be looking at fuel mileage as a goal - not beating the guy in the other lane to the next stoplight.

They are (again, hopefully) more dedicated to maintaining their vehicle properly. This makes all the difference in the world. When people mention their desire to own a Roll Royce, for example, I tell them that they (the Rolls, not the person ) are the most lovingly hand crafted P.O.S. ever made. I tell them that if someone bought a Ford Pinto when it was new, and then proceeded to lavish upon it the care & nurturing that a Rolls receives, it will last just as long. (Actually longer, but I don’t usually want to upset them *that* much )

Thanks for the opportunity to rant & ramble.
RTH