I was thinking about this the other day, and it's really all about status. You don't buy a BMW because you think "this is a great deal and a great piece of engineering, what a great and practical use of my money!". You do it because you want people to know you have a BMW. Which I guess is great if you associate with the kinds of people that care about wasting money on perceived social status, but absolutely doesn't make sense if you care about making a smart financial decision.