<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Brendan:
Given that NO airline flies nonstop DEN--Australia, one does have a choice of several airlines/alliances that do it with one (or 2) stops.
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Okay, maybe taking DEN-Australia in a vacuum is a bad example. If that is the only route you ever fly, then you're right: you could choose either UA or AA (with partners) and get there in about 22 hours.
But if you live in Denver and want to pick one primary carrier that you use for a wide variety of travels, you have only one real choice. (You can also choose to not give loyalty to any one carrier, something most infrequent travelers already do.)
The only point I'm making is that the vast majority of people don't have two carriers to choose from that are so equal in every way that the FF program becomes the deciding factor - with Chicago being the notable exception I can think of off the top of my head.