They aren't good cars. They come from England! Have you ever seen a good car come from there?

Just kidding. Actually they have a pretty poor reliability record.
Let's see... You said 30-40k miles, 2-3 years old, and they are 40-60% off of the new dealer price.
2003 Jeep Grand Cherokee Limited ~$38,000
2000 Jeep Grand Cherokee Limited (same options) with 27,000 miles ~$20,000
The Jeep depreciated 48% in three years.
2003 GMC Yukon ~ $45,000
2000 GMC Yukon (same options) with 30,000 miles ~ $25,000
The Yukon depreciated 45% in three years.
This is very typical for most cars. Most cars will depreciate 50% after 2.5 years with average mileage (10-15k per year).
For this reason, you'll take a much bigger loss if you spend a lot more for a new car. If you spend $60,000 for a car, 2.5 years later it may be worth $30,000. You've lost $30,000!! If you spend $8,000 for a new car, 2.5 years later it you've lost $4,000.
Also, new cars depreciate faster than used cars. If a car loses 50% of it's value by the time it reaches 30,000 miles, it may take another 100,000 miles until it depreciates another 50%. As stated above though, if the vehicle is only worth $8,000 when you buy it used with 30,000 miles, you will drive it for 70,000 miles before it depreciates another 50%, and you don't have as much money invested, so losing 50% on your investment isn't like losing 50% on a new car.