The outer skin of a car supplies no structural strength or accident protection so it's a natural place to save weight and yes money. Sports car makers have been doing this for years to reduce weight. I like the feel and sound of a heavy door or hood too but the X5 would be even heavier than it is if the panels were thicker. Maybe they went too far but I think that's the direction most manufacturers will be going.

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Porsche 996 Turbo (Ruf 550)
Porsche 993 Cab.
Porsche 997 GT3
Audi A8
BMW X5 4.8 White, Black Napa, Sport, Technology, Premium, Prem. Sound, Cold Weather, Rear Climate, Multi-Contour, Sirius, HD Radio, Running Bds., Bamboo