But here exactly is why it's murky. Are there are 2 sides? Not if the airline determines there isn't. Look, you were accorded a Y-seat on your preferred flight in return for accepting to have D points deducted and blended-in with the balance of your itinerary. The extreme response would be for the airline to decline to allow such bookings on flights that are not available in D, and then you'd be looking at fewer booking possibilities.

This is why the decision to first take care of its regular premium customers makes sense. It still allows D-paying customers to standby, however, such a customer already has been accorded a privilege (being booked on the flight in question to begin with).