Delta says it, like other airlines, offers all seats on planes to frequent fliers, just at higher mileage cost than the lowest redemption level, which is 25, 000 miles for a domestic coach round-trip ticket.
But if you want to sell back Red Dead Redemption, Mass Effect 3 and Skyrim to help you pay for half the cost of a physical copy of the game on launch day, I suppose you have that right.