I somewhat get "it" on the mileage thing; depreciation, yadda yadda, yadda. However, there is a BIG gap between 12,500 and 40k miles a year and a lot of us fall in the middle.
Before buying my TDI I did LOTS of research (including signing up for this site) and trying to make a wise decision based on my 80mile a day commute to work. At the time, the Passat was the Motor Trend car of the year and receiving quite a bit of praise - specifically for the diesel version. For it's part, VW sure didn't mind playing up the award and advertising their "balance between long range and driving fun."
I say all of that to suggest that -if VW really does have to use the mileage factor at all - they really should have had to put more effort into finding a true average of miles driven by TDI owners and use that for the benchmark rather than use some nationally calculated average. Their marketing catered to people wanting to drive their cars more miles, but now those same people are going to get less in the settlement regardless of how well they kept up with their maintenance, repairs, condition, etc.