Ezra Klein (sorry – permalink seems a bit funny) in which he notes that a “cheeseburger at McDonald’s is 99 cents. A double cheeseburger is…100 cents.”
To me, this looks like classic price discrimination. The two products are (for all practical purposes) priced the same. One is a much better value than the other, and McDonald’s has reason to believe that its less price sensitive consumers won’t notice. Or is there something else?