Oh cool, I had no clue. Wikipedia says they share 20% of the same parts.
Your knowledge knows no bounds....
VW used an existing chassis for the Bentley Conti GT and Flying Spur, I believe it was the same chassis as the A6, I'm am not sure. And they still share chassis, and engines.
The Germans are going use their existing chassis, they are not going spend billions engineering a whole new chassis. Remember Rolls doesn't come out with new products often, their product life last a long time. The current Phantom has been out since 2003, and they just "updated it".
VW has taken a different strategy with Bentley. They have the marque come out with more products, and a shorter time line.
The two cars I believe that looked like VW and BMW thought that they could make the best of the same car would be the Bentley Azure/Brooklands Coupe and the Rolls Phantom Coupe.
Both have that upright look.