Although it does answer the OP's question of whether one is EXPECTED to tip at this type of restaurant. Whether you do or not, and how much, is still up to the customer. It actually makes sense to remind people in an airport, where people may be passing through and aren't aware of American customs for tipping.

One of the things I always check before traveling to a country for the first time is tipping norms, so as not to over or under tip. But I'm not sure I'd think to do that if I were in transit. I certainly didn't do that for my connection at IST a few months ago (although I knew I'd be in the TK lounge anyway).