I drive an old Mercedes Benz sedan - its pretty gray haired now, nearly 288,000 kms on it. I use mobil 1 0W40 in it and change the oil at 24,000 kms (I drive on the highway a lot - 104 kms one way to work) - so it alerts me to change oil at that mileage - The engine is fit at a horse, neat n clean too, no sludging or buildup.
OTOH I repair MB transmissions as a side income, this gives me first hand one on one dealings with european car workshops, 100% of sludge failures is failing oil change at correct interval, One 528i came in for oil change at about 40,000 kms - the oil was sludged to hell. (YES........ I know BMW should be ashamed of themselves for not specifying permanent oil in their engine crankcase ) - car was out of warranty too
I have seen some ML class benz like that too (engine breathers leaking like a sieve and eventually turned the oil into tar - siezing the engine solid locked) - customer said - an oil leak shouldnt do that - thats why I never had those covers resealed - umm lady them covers are the PCV of this engine - no breathing no oil cleaning. (facepalm)
Tons of toyota 1MZ and 3MZ engines - aka sludge monsters, aggravated by mommy only going to the store in the car - run cold and yes the engine will sludge up. (both in lexus and toyota badges)
audis too.. but havent seen much of them in those shops because they are mostly liked up north in USA where it snows.
I do know of the full paid for maintenance - I have that in my household nissan too, Its no where near the price to the euro cars but still the dealer gave me that when I pushed on it.
As I said - its not even simple as going to a store and eyeing the viscosity numbers only, the BMW LL-01 oil or mercedes benz 229.3 and 229.5 oils are a very rare item and usually cost more than the average synthetic 5w30 API SN that you pour into your chevy/toyota/onda. Their differences start from base stock and go right into the add pack.
They are blended differently to actually pass those gruelling tests. Its not even just engine oil limited to these tests.
difference is that oil of yesteryear and today is very different.