to make the blanket statement that "All cars decrease in value" you ignore that certain collectible cars (since you say "all" I can include a Max Wedge 63 Plymouth, or a Super Duty 62 Pontiac Catalina or certain low production import cars) have gone up quite a lot in value, and that takes into account inflation.
As for modern cars, there are examples where cars that have been discontinued have had the typical price that they sell at (usually discounted) go up slightly (maybe not discounted as much or at all) for a short period of time. With very rare exceptions though, they will go back down again when the buying frenzy is over. In one local example, when the Pacer was killed one local dealer quit dealing and asked sticker price for one on the floor (Yes, I actually considered buying one if the price was right). I didn't buy that one, but it did sell, at sticker a few days later. The dealer was betting that some AMC fanatic would buy it to save, and that may have happened. We can be sure though that the car didn't bring big bucks, but if it is sitting in a garage somewhere with 10 miles on it in new condition, it will bring much more than new price at auction, but probably not equal to inflation, not that kind of car.
Anyway, be careful of blanket statments like you made, they are usually wrong.
