When I asked how often this happened, there was silence. Which leads me to believe -- as does previous anecdotal evidence -- that it happens basically never, and the people who bought the pizza were as confused as anyone else. It wasn't protocol; it just felt right.
But it also leads me to very, very firmly believe that if your flight is delayed, you should get pizza. Of course, like anything else, the novelty will eventually wear off, and you’ll need something more. Steaks at the gate; lobster for Platinum Preferred members. But let’s worry about that later.
The point, for right now, is: if my flight gets delayed, give me pizza.