Well not as much because BMW make one brand of car, you go in a chose which model you want and thats it. The engines for example may be the same but its still a BMW engine (with the exception on the Mini).
With Audi the parts are not only shared across the Audi range but across various marques and if you dont think that matters then read this as to some people it obviously does.
http://www.time.com/time/specials/2007/article/0,28804,1658545_1658544_1658539,00.html
The fact that everyone's doing a similar thing yet Jaguar are failing and VAG etc. are not, should tell you that brand conveyance is more important that the behind-the-scene facts of what goes on in the production and purchasing departments of these car companies.
In my mind's eye, Audi holds more prestige than BMW and your part-sharing argument is entirely defunct as BMW do exactly the same thing.
Everyone shares parts, it's how the marketing and conveying of the brand image is achieved that matters. Jaguar failed in this, Audi and BMW didn't. That's all that your Time quote serves to highlight.
Those young Jaguar buyers went off and bought an Audi or potentially a Bimmer because Audi and BMW have done a better job of conveying the image, not because the car part sharing was more acceptable.
If VAG suddenly ditched their subsidiary brands and called all their cars VAG x, VAG y, etc., they would be in the same situation as BMW in terms of it suddenly becoming acceptable to share parts just because they're now all branded the same. Whether parts are being shared between entirely different marques or just different models is an entirely arbitrary comparison and does not hold any weight in a sensible comparison of prestige.
Jaguar are not relevant as they tried to turn a luxury English brand into an American Mondeo. Audi have done no such thing.
This thread has made me laugh, Robbie G should consider going on stage his views would get many many smiles.....
I'm glad that my views amuse. Potentially you would add more to the discussion by airing your own rather than trying to pimp my stand up comedy abilities.