Working for GM I replaced quite a lot of engines.. You would be AMAZED at the amount of people that have NO CLUE that their engines have oil, much less that it needs to be changed.. I pulled MANY vehicles onto the lift and raised them up to find they still had the original oil filter on them, with 50 to 80 THOUSAND miles... Pull the oil pan down, and it leaves an impression in the sludge where the oil pickup tube was.. the oil is solidified to the point I could pick a gob of it out and form it into a ball..
Changing the filter might help... that half to one quart added may have rejuvenated the oil enough to let it keep going... What I know, is that I change oil every 3000 miles. It gets rid of the ash and other build up in it.. sort of like rotating old brood combs out of a hive.. Stuff you do not want DOES build up, especially if you drive like I do.
The other issue is the oil bypass valve. Once the filter begins to plug up, the oil bypasses the filter, and is not even filtered. The first thing I do on an engine I rebuild for my own use, is block off the bypass, and install dual remote filters. The 89 truck I wrecked a few years ago was closing in on 300 thousand miles, the one I have now is about to roll over 150 thousand.... but I replaced the motor with a roller cam 350 at 91 thousand.
I have no arguments with anyone running their cars as they wish.. like keeping bees, we all have our own methods..
My wife has a New Prius Hybrid, and the service interval is at ten thousand miles...... Umm... no! I still change the oil in it at 3000.. She will likely drive that thing until it wont run anymore, or we cant get the parts to fix it. Something in me just wont allow me to let a vehicle get that many miles before I change the oil....
A friend of mine in Maine bought a new toyota truck... ran it for 120 thousand, and then sold it to another friend of mine... the first friend NEVER changed the oil.. as stated, he changed filter and topped it off.. when the second friend bought it, he changed the oil, said it was NASTY when he pulled the drain plug... it ran 2800 miles and started knocking... lower end knock from a bad bearing.. Yep, he got 120K out of it... Got his moneys worth, but I have seen well maintained toyotas with over 500K on them.
Being one of those people that refuses to pay the idiotic prices for a new truck.. I will keep my oil changed, and keep on driving my old one for as long as I can scrounge parts for it!