[Dean]

AFAIK the only thing hub centric center bores are good for are lining things up when installing wheels. Priceless on lug bolted cars like the A4. And providing a little support in the event of loose lugs/bolts so they don't just shear off and drop the corner of the car to the ground. I can attest to the later as well having been in a car at the track with loose lug bolts.

And as far as studs vs. bolts, I think the German engineers convinced the TUV at some point that bolts had some small benefit and thus the TUV made it a standard for cars they certify or some such. Not that interested to go research it but that is what I recall when I asked back when I bought my Audi.