Where do they recommend using anything other than their own oil? and do you have any proof that it is the same stuff? I highly doubt it is and would not be persuaded otherwise without proof.
Ha, hope I haven't opened a can of worms here... the source of this 'info' was the owner of my local dealership, a few years back he was telling my Dad, a Merc owner, about all the different suppliers/manufacturers etc. and that if bought directly, basically not from him, you would make a saving on service items - and that was from the owner of the place, so go figure
I distinctly remember him saying that Fuchs supplied most of his groups fluids - at the time Audi, Merc and VW. I use the branded stuff VW recommend but where they don't I use Fuchs.