In the days of carburetors diesels did INDEED outlast gas engines with the exceptions that are always experienced.

The BIGGEST reason for the delta was that the carburetor was dripping raw fuel down the cylinder walls duriing cold start ups. This acted as a solvent stripping the oil film.

The intake valves do not last longer because of fuel going over them. In a gas engine things occasionally happen that cause a lean condition that will burn valves. This is not an issue in a diesel.

Yes the diesel fuel is nothing but light oil. The byproducts of diesel combustion is an oily soot rather than abrasive carbon as in a gas engine. This not because diesel is an oil and gas is a solvent, rather the carbon by product being the abrasive.

Now that we have fuel injection gas engines, I think that an equal quality, equally well cared for gas engine will last about as long as its diesel counterpart.

My $0.02,