Link to Award Application.
http://www.mbusa.com/media/downloads/main/heritage/High_Mileage_Application.pdf
I don't think you will ever see them in miles.
Besides Kilometers looks way cooler ! The numbers are bigger.
Curious though - they have a 1,000,000 KM award and then one more - for 1,000,000 Miles.
Maybe that is the only one. One Million Mile Club !