Originally Posted By: salv
It isn't the engine design. It is the recommended oil. Volkswagen calls for a 5w40 full synthetic, and the OCI is based on the factory fill Pentosin.
If you are going to run an off the shelf group III, count on 5k to 7500k intervals.
The TDI's use 5W-30. The VW factory fill is Fuchs. Most Euro Synthetics these days are HC Group III oils.