I believe part of their reasoning is that the premiums are donations, given voluntarily, and there is no requisite benefit. On the other hand, they've made it a requirement for when you pick and what seats you can pick (yeah, it sounds contradictory to me too). What they appear to be offering are choices on payments made for the actual tickets purchased.
That's the best explanation I can give you. Perhaps some of our accounting/tax experts/lawyers can give you a more definitive.
I've probably just clouded the situation more. Sorry.