It's what the market demands. Wealthy people want tractors with poke, so they have the BMW X5 5.0, The Coming Porsche Cayenne Turbo S, Range Rover Sport, formally the Merc AMG ML55 now replaced by the ML63. VW also have the Toureg with the V10 TDI which is a brute, and the upcoming Audi as well. Remember these customers usually have a Porsche, Ferrari etc already in the garage, so they want their everyday car to have lots of go too. If they can afford it, why not :)