That never was the question. Here is the quote
"As a car ages, more frequent changes might be in order, but that's for a qualified mechanic to decide on a case-by-case basis."
Modern oils hold the fine dirt particles that the oil filter do not remove in suspension. But oil can only hold so much dirt. If you change oil often enough the oil changes get rid of the dirt. If you don't change the oil as often them some of the dirt will stay in the engine. If every oil change you leave some dirt in the engine it adds up. This does not require a Ph.D. to comprehend. Examining an old car and determining whether the engines oil needs to be changed more frequently is not the intractable and difficult proposition that you are making it out to be.
I have seen plenty of examples where car manufacturers provide recommendations to mechanics in one form or another to examine the oil and engine to determine if the oil has been changed as often as it should be. Typically this sort of advice comes in service bulletins that are intended to help diagnose engine noises like valve train clatter. More often than not these descriptions do not go into any particular detail of how the mechanic is to make such a analysis. It is assumed that a competent mechanic can tell the difference between a clean engine and one that is not.
-jim