I think as others have said, their needs to be a clear distinction between luxury marques.
Tier 1) rolls, bentleys, maybachs etc
Tier 2) Audi, BMW, Mercedes, Lexus, Porsche
Tier 3) Acura and Infinti
This brand distinction isnt particularly clear since if you look it at, platform sharing between the luxury marques (ie VAG) and between marques and their parent group (ie Bmw and Rolls), but this is the best you can figure.
Now if you look at Tier 2 mfgs, like Audi, Lexus, and Porsche, your stuck at sticker, or maybe a 1% off sticker, they dont negotiate mostly, unless its model end or something like conquest cash comes about. Bmws and Mercedes the negotiating headroom is much better. Bmws and mercedes can be had for 500-1000 above invoice, which is about 6k off of sticker. These two dont get stuck at msrp, since they are two companies that dont offer economical alternatives. Example VAG: If you want a family SUV/SAV your choices are: Economical VW Tourag, Luxury: Audi Q7 Performance: Porsche Cayenne. Hence, why negotiate, they offer the same vehicle platform, in different flavors from different marques.
Now when it comes to BMW, they only offer one marque, and they can do the same, but with different option sets (Base 528i, 535i, 550i) hence you get your three choices, all from the same brand, and diff price points. So in my opinion, BMW 5s arent really priced high or expensive, they offer what they can in the Luxury domain, and that too at an affordable invoice price, which is far less than what the others can do.
Now if you compare different tiers, theirs going to be an obvious stick shock/outrage. My thing is yes, BMW do offer less, then say Acura and Infinti offer, but you have to see where each manufacturer is coming from. If you look at my sig it explains a bit, but if you look at Acura, their cost to build a RL is going to be far less than a 5, since they share basic architecture from the Honda vehicles they are based on.
Sorry for the long, convoluted read folks!