<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Paulo:
But it does raise the question - particularly for the NW policy - if you can upgrade at the time of ticketing on full Y, then doesn't the full Y fare become the de facto F fare? Who would ever buy F if you can fly in F for buying Y?</font>
A paid F-ticket has other advantages as far as complete refundability & changeability, etc.