Is the global real estate boom losing steam? Are developers so desperate to move units that they have to give away a luxury sedan to close a sale? Not likely. Then why are sellers of new homes in places like Dubai and Hong Kong offering a brand-new Tesla Model S with each purchase?

Offering some sort of prize or premium with a new home (sometimes a car, sometimes a luxury vacation) is a time-honored tradition in the real estate biz. Like so many similar sales pitches ("If we can't sell your house, we'll buy it!"), a little common sense will tell you that it's a gimmick to make the phone ring, not a transaction that's ever likely to take place. It's safe to say that few, if any, of the buyers who respond to these offers will choose to take delivery of a new Tesla (simply negotiating a cash reduction in the sales price would be a much better deal for both buyer and seller).

However, if the recent spate of "free Tesla" come-ons reveals nothing about the real estate market, it reveals something very interesting about Tesla. The American electric car brand has become a universal global symbol for luxury, like gold and diamonds, Champagne and caviar. In the US for many years, the automotive embodiment of affluence was Cadillac. How many books, songs and popular sayings used "Cadillac" as a synonym for luxury? "I bought you a brand-new Ford. You said, 'I want a Cadillac!'" sang BB King in his 1963 hit How Blue Can You Get?