JS,

I didn't mean to suggest that the walkup v. 3 week advance wasn't essentially price discrimination. I think it clearly fits the spirit of price discrimination. What I really meant to suggest was that the higher price for direct v. connecting flights was also essentially price discrimination. I would think the cost of providing connecting service would be higher, but it's sometimes priced less b/c there are people willing to pay the premium for flying direct.

I just think that one person's convenience is another person's necessity. Some people are willing to pay more for a direct v. connecting flight. Similarly, some are willing to pay more to avoid having to plan in advance. I agree that having to plan 2 or 3 weeks in advance is certainly much more onerous than a connection, but there are certainly some people willing to do so (e.g., leisure travelers). For others, they're willing to pay the premium to buy a ticket at the last minute (just as some are willing to pay the premium to fly direct when that's more expensive).

The point about the strict defn of price discrimination was just an irrelevant nit. You could make the case that the products in your examples are not identical. The full fare tickets are, in some sense, of higher quality. They don't require you to plan in advance (and are also fully refundable, although that's perhaps a different issue).