Obviously cost per seat mile is cost per seat, per mile. Of course it is based on a full airplane. Otherwise it is not possible to compare cost between aircraft types for a specific route. Profitability is determined by load factor, ticket prices and resulting yield.
Cost per seat mile includes all type specific costs like capital cost, maintenance, reserves, fuel burn, crewing, training and many more. I am sure Boeing disclosed in their sales pitch how they came up with their numbers.
Last edited by GTC58; 14th Feb 2013 at 23:58.