Let's look at this in some detail...
That's EXACTLY what it is. "Image". You're paying your extra GBP 20,000 for the "image".
Now, I walk into a BMW showroom for a four-door, high performance diesel......
Me: I want to buy a twin-turbo diesel please.
BMW Salesman: OK, we have a 535d with 313hp for sale. That will be GBP 44,290 please.
Me: Hang on a second, what's that car over there? It has less interior space and is not as practical, but it looks better than the 535d. I'm willing to compromise on space a little if it looks that good. How much is it?
BMW Salesman: Oh, that's the 640d Gran Coupe, and that will be GBP 63,900 please.
Me: Er, OK. That's nearly GBP 20,000 more than the 535d and yet it offers no obvious advantages other than it looks sexier. In fact, it's a bit compromised on space compared to the 535d.
BMW Salesman: Yes Sir, but that is a 640d. See? 640d.
Me: Oh right, so it has a different engine to the 535d?
BMW Salesman: Er....no.
Me: OK, but it must have more power then?
BMW Salesman: Er....no.
...
Me: So the 535d has 18" star-spoke wheels like the 640d?
BMW Salesman: Er...no. 17" is standard. 18" star-spokes on the 535d will run you GBP 1440 [running total: 45,730]
Me: The 535d comes as standard with DVD multimedia, navigation, BMW Assist and a 10.2" display?
BMW Salesman: Er...no. Standad would be CD, no nav, no BMW Assist and a 7" display. That other one on the 640d will cost you 2,090 [total: 47,820]
Me: Same BMW Business speaker system?
BMW Salesman: 415 [48,235]
Me: Folding auto-dimming mirrors?
BMW Salesman: 250 [48,485]
Me: Xenons and headlight washers?
BMW Salesman: 920 + 215 [49,620]
Me: Voice control?
BMW Salesman: 235 [49,885]
Me: Brushed aluminum trim?
BMW Saleman: 240 [50,095]
Me: Split-folding rear seat?
BMW Salesman: 390 + 45 for the requisite 12V socket [50,530]
Me: Sport multi-function leather steering wheel with gear shift paddles?
BMW Salesman: 110 [50,640]
Me: So you're telling me that the price difference between comparably equipped 640d and 535d models is actually closer to 13k than 20k, with the 6er GC costing about 26% more than the 5er. And that the "20k more for the image" is not quite accurate, but that part of the 20k difference is actually due to a higher standard feature content, is that correct?
BMW Salesman: Yes.
Me: And that difference is roughly comparable to what Mercedes charges for a CLS 350CDI Sport w/7G-tronic (£53,500 OTR) vs an E350 CDI Sport w/7G-tronic (£39,250 OTR), with the coupe costing £14,250 (36%) more, correct?
BMW Salesman: Seems like it.