In terms of sheer numbers, that is true, but I'm guessing that as a percentage of total sales, BMW does not sell as many four wheel drive cars. Also, the XDrive has its merits but in different contexts it doesn't perform as well as other four wheel drive systems. Unfortunately, there's no four wheel drive system that can do it all: heavy offroading, gas saving, low friction, etc. The Torsen is more capable than XDrive offroad, as evidenced by this video:

vid 1

But then in other situations, Torsen is limited:

vid 2

Which four wheel drive system is better depends on what you want out of the car. Hence, the reason why the X5 is called an "SAV."

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