I agree that it seems unfair that the second empty seat would not earn FF miles, but I think that the rationale is that there is still a single person making the travel. If they awarded FF miles to the empty seat, essentially a non-existent person, then I think this would open the door to violas being able to earn miles or, people flying might buy another seat to get double miles and theoretically a person who may have paid more for the seat could be bumped due to claims on available seats. I think that FF miles are an incentive to continue to fly the airline, and I would hazard a guess that the airlines don't feel that the empty seats are deserving of incentive.
[This message has been edited by CozumelJen (edited Mar 25, 2004).]