Earlier quoted context omitted.
If you take these corporations to court these arguments don't stand up. In your oil example, if you had a warranty claim due to say a broken suspension component then the type of engine oil used wouldn't be relevant. It just allows them to try to weasel their way out of claims.
...that is exactly what I said? Dealers will(and do!) just reject any warranty claim based on the fact that you haven't serviced the car with an official dealer. You can show them all the documents and laws and they will just ignore you. Taking them to court works but it just ends up costing you time and money.
they make money from regular service as well and want you for that. However warranty work is too valuable to them to ignore