I just finally used up my initial 1,000 mi from purchase. I was tracking everything in Teslafi (except for one super charge, which I will equate to 5 kWh). I can see I got a little over 405 kWh for those uncharged miles. My consumption was approximately at 285 Wh/mi (lots of 80 mph interstate driving) which means that, effectively, I got a little more than 1,400 mi.My guess is that Tesla marketing gurus overruled the engineers and said nobody thinks in free KWHs so lets just call it free miles. As long as everyone gets more miles than 1000 nobody complains.
If this was supposed to be 1,000 mi, the assumption must have been 400 Wh/mi.