There's something I recall from the universitee about monopolies. Making money. Its either called the "controlled monopoly" or the "perfect monopoly". But it is where you have a large audience of buyers out there, and they all have different amounts of money they are willing to spend on a product.
You can make the most money if you get everybody to spend exactly the amount they can afford to spend. Ideally, you have the exactly the same product, say an Izod shirt. In the boutique, you sell the Izod shirt for $75, and the wealthy buy it. In the mall you sell the same shirt for $50, the average Joe buys it. In the discount store you sell it for $25, the bargain hunter buys it. This sales model will make tons of money, as tons of different people will buy it.
Porsche has the same opportunity with the Boxster, Cayman, and Carrera. those people who have $80,000 to spend on a Porsche will buy a Carrera. Those with $120,000 will buy a Turbo. Those with $50,000 will buy a Boxster.
Then you roll in the Certified pre-owned cars, and they increase the number of choices that the buyer has for a particular price point... making it all the more likely that they will find what they like at their price point!
Great job, Porsche! You did your economics homework! (AND your Physics, art, and engineering!)