I don't think they're quite as rare as they make it sound. It seems like half the restaurants in NYC have one. Though I would believe that most people who have seen one didn't realize what it is.
"Half" is almost certainly an exaggeration, but there's probably a few places on Wall Street that serve $200 steaks or whatever for lunch regularly that have one. And it probably gets used only a few times a month, if at all, and they consider it an advertising expense.
Disclaimer: I was a programmer for Bloomberg, but I never saw one in a restaurant.