They don't need it, but their customers might. I always imagined it was like in movies about rich people in the 80s where the waiter would interrupt the lunch with a note on a silver platter, and they run off because Saudia Arabia just cut oil production and oil futures are going crazy or something. But wait! They don't have to go all the way to their office because there's a Bloomberg right here!
"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.
The Bank of America branch on Sand Hill Road in Palo Alto, near the headquarters of the major VCs, had a public access Bloomberg terminal in the lobby for a year. May have been a marketing demo from Bloomberg.
Making a reservation or ordering food from Bloomberg Chat actually sounds like a feature that would be used by a lot of traders. I doubt that there are many restaurants that have a Bloomberg account though (there is no need for a physical terminal, Bloomberg Anywhere can run in a browser).
