Where do people come up with this? As long as you're using a OE equivalent, your warranty is just fine. You actually think Mercedes makes ALL their own parts? There are all kinds of OE vendors out there that produce 'Mercedes' parts... Mahle, Mann, Bosch, Litens, Hepu... the list keeps going and going. Same thing with VW/Audi and all the imports for that matter.
Stop spreading misinformation.