Someone earlier asked why Chrysler/NeedsWings wants to know the mileage on the car. Someone also posted all the TSBs on these forums (Technical Service Bulletins).
One of them (06-029-03 Subject: Replacement Keys) has steps for the Technician to order replacement keys.
This is something they access via their DealerCONNECT system, to process the order with the "Key Production Facility".
In Step 7, just after they enter the VIN, it says "Type the mileage".

So it's needed by their system in order to generate the key order. It doesn't say what they do with the mileage, in relation to generating a new key though.