Dan I partially agree with you. Oil technology has come a long way from what it was back in the 50's and 60's. So more frequent oil changes were the norm back then to keep engine enternals from sludging up.
But even though engine tolerances weren't as close as they are today, and older engine designs naturally wore out quicker because of that fact, a well maintained engine (even from the 50's and the 60's) actually lasted much longer than most people thought they did. Why you may ask, and what caused this misconception?
Because back then "clocking" or turning back the odometers was rampant at ALL car dealers. Any used car that came in, and was well taken car of by the previous owner, but may have had a few more miles than it looked like it had, was an automatic candidate for the mileage removal surgery.
The dealers didn't even give it a 2nd. thought. And for the most part, the buyer was none the wiser. But the end result was the next owner usually wound up rebuilding the engine at a 100k when it really had 50% more miles on it.
Thankfully in the 70's, most states started including odometer statements with the titles, that helped curtail this practice. Facing the possibility of stiff fines, and even jail made dealers think twice about clocking mileage.