[Dah00n]

>If your fuel quality is crap, i.e. has any ethanol in it, you will need to replace your oil more regularly

That is real-world use in most of Europe and is included in the higher mileage between oil changes compared to the US discussed here. I don't even think most Europeans inside the EU have access to ethanol free petrol? At least around here (Denmark) it would be illegal. If a car breaks down because of ethanol in the petrol it is of course covered by the manufacturer. Otherwise they might as well state "warranty 5 years but not if petrol has been added at any point".

The manufacturer specified intervals are just fine and you'd need to be an extreme outlier to have any problems with your oil following them. Maybe if you have a caravan attached at all times or drive off-road or racing or all of the above at the same time. Otherwise consumer law would mandate the manufacturer pay for any damages caused, as it damn well should. It is also the manufacturer that would have to prove the fault is yours. Not possible if the car have been serviced even if done by a third-party shop. The oil would have to be visible damaged even if looked at by a granny (they cannot demand you understand oil better than "it looks like oil and is inside the specified mileage").