Cars typically show the highest dollar depreciation in the first two to three years of life. So it's not surprising to see a decline in value no matter which service is valuing the car. I know a couple of people that take advantage of that fast drop in value by buying 2 year old used low milage luxo-mobiles like the Volvo or Mercedes.

Given that a new car loses so much value in the first two years, I find it hard to understand a sellers motivation in buying new every two years. The longer that car is driven before sale the lower the cost of transportation will be.