Well, that's exactly my point. The future value of any vehicle (X5, C300, etc.) can't be accurately predicted. So unless you are confident that you will keep the car vehicle for 5+ years - why not lease?

Let's say that the X5 in question was leased 4 years ago and BMW Financial Servies used 45% residual that was common back then. Now you want a new car and the current value is only 38%. Wow, you saved ~ $3,500 plus you had no trade-in issues. OTOH, what if the current value for the X5 was now 50%. Wow, you can buy the car from BMW and sell/trade it for a nice profit of ~ $2,500.

Leasing is not for everyone, however if you only drive around 15K miles/year and you are uncertain of your future automotive needs (or like to get shinny new cars like the C300) - leasing is a good idea.