It's not cobblers. 25 years in the car trade and I'd say stereotypes generally hold true.
Based on my experience of going around showrooms, I'd say that some of it comes from there.
I was going round showrooms to decide which company car to get. I made clear at the outset that I couldn't buy from the showroom but only from via the company car fleet provider.
I found VW to be friendly, engaging and interested in showing me vehicles regardless of whether they thought they were going to make a sale.
I found Audi to be standoffish and arrogant, kept me waiting for ages, then not interested in showing me anything at all once they knew no sale was in the offing, keen to make out that they have hundreds of different models etc.
Mercedes were better than Audi but no-where near VW. Mercedes world again kept me waiting a long time without any acknowledgement and weren't very interested in showing me their cars.
Skoda were OK, but confusing - they have a version of the Enyak that you can't actually buy.
I think most of the mid range manufacturers are just keen for you to look at their cars and like them. I've found Renault to be friendly in the past. For Merc and Audi particularly, if there isn't a sniff of a sale and you don't look like the "right" sort of person, don't come in and go "i want that one", they are not interested.