I began noticing this about seven or eight years ago when the oil filters I bought changed from official ones to obvious counterfeits (certain pieces were missing entirely + media was much thinner than the real ones). Had to switch to a local auto parts supplier to guarantee the correct part.
How did you notice that the media was thinner? On passenger vehicles at least, the filter media is in a stainless steel cup that precludes examination.
BMW at least has the media completely exposed. There is no canister like you might find on Honda oil filters. Basically on BMWs the oil filter housing is permanent. I don't think it's a BMW specific thing. Might be a German car thing?
Toyota Tundra filters (at least) are the ‘innie’ pieces, and the cup is a removable/reusable part on the vehicle. A counterfeit would be pretty obvious unless it was at the microscopic level.
