I think something similar applies in many parts of the world, _but_ I also think that the response from the OEMs is basically "fight the warranty claims hard when there is third party service involved, and just honor the warranty with a smile otherwise". Basically malicious compliance is what they have to resort to. And as a car owner I'm lazy and afraid of conflict. So I happily pay X% more for the service to get the no fuss warranty (And the OEM shop is even happier).
In order to deny a warranty claim the US, the manufacturer has to prove the issue has been caused by a modification or servicing.
Why would anyone want to service their call at a stealership? The prices are unfair and the quality of techs is awful. Better to find a small reliable shop.