You guys pretty much hit the nail right on the head. There are many more factors to think about in a replacement airplane than a one for one exchange of seats. Aircraft acquisition cost, operating cost, route structure etc all come into the picture.
We bought the 767-300's because they were the best bargain for size, cost, maintenance, and so forth. In addition things like maintenance contracts and training contracts also enter into the final cost. Even if we don't carry as many people per plane, all we have to do is increase frequency to make up the difference. We've already done some of that now. With the DC-10's we had three daily LAX - HNL round trips. Starting this summer we move to four with the 767's. In the past we had eleven weekly SEA - HNL trips. Now with the 767 we are running one daily SEA - HNL and one daily SEA OGG (maui) trip for a total of fourteen weekly SEA trips. Smaller planes, but more frequency. And the good part is if the loads fall off we aren't losing as much money per plane as we would have with the DC-10.
If we had bought the 767-400 we would have had about 50 more seats per plane, but at a much higher acquisition cost, higher operating cost, and a bigger exposure to loss if the flight isn't full.
As for our seating capacity, it is 18 F/C, 234 Coach for a total of 252.
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.