Most service cars are polo's and ups because writedown on them costs £200 a month instead of £700 a month on tiguan/performance golf/beetle cab etc. Most service fleets run a couple of larger cars and a couple of automatics for customers that request something bigger or only have an auto licence but of course booking times can be extended.
Virtually every dealer has 1 of every car on demo though so if you want to buy or experience one then its easy enough to arrange a test drive. I can understand why a dealer doesn't hand out their R for a service customer that "just wants to try it" as for the 2 days its out then there isn't one for any customers who walk in to try. The expectation for the customer to show some interest and dedicate some time to booking the test drive seems reasonable.
Also comparing a vw service department to Porsche is a bit like comparing macdonalds to the savoy. Margins, volume and product range are completely different.
