I sent an email to Servicehelpna @ teslamotors.com on 8/18 requesting clarification as to why I received the letter (again, I have only used my local supercharger once, but have been on a number of cross country trips in the last year and have visited more than 40 unique superchargers). I have yet to hear back.
I do have an excellent relationship with my local service center and mentioned the email to them. My SA assured me that I did not match the qualifications of the intent of the letter. But still, this letter came from corporate - a clarification from corporate would be nice (I am assuming that local SA had no idea I was a recipient until I told him). I do worry that I have been 'flagged' in some way - I would like my record expunged.
Blue Fire may be onto something here. We have 23,500 miles on our car in 15 months, of which about 15,000 is from road trips and another 3,000 for business trips to Modesto or to conferences in San Luis and Palm Desert. So, we have only charged about 25% of our mileage at home, and maybe 10% of the electricity on road trips is from other sources. So, in a vacuum, I am charging close to 67% at Superchargers. Maybe the sole discriminant in determining recipients was percentage of Supercharger usage regardless of location.
(As a side note, it is nice to hear that you enjoy a good relationship with your Service Center. Tesla just routes me wherever, so I have not had the chance to cultivate a relationship with a soul.)