Comment Delta had no choice (Score 1) 303
Carriage laws in the US prevent a ticket price from being changed after it is purchased. This includes canceling the ticket because of the price it was issued at (because this is effectively the same as changing the price of the ticket since the consumer would have to repurchase it). You'll notice that Delta's carriage policy specifically outlines that they will never sell a ticket for $0 so they can excluded it. Since they can't state this for any other fare price, they can't exclude it and it falls under the general carriage policy.
http://www.delta.com/content/dam/delta-www/pdfs/legal/contract_of_carriage_dom.pdf
It would be different if, say, Kayak or Expedia screwed up and gave the wrong ticket price... but since this was on the carriers website and they are dealing directly with the customer, they are SoL.