This answers a lot of questions. I happen to prefer Coke Zero, but you have to admit, it's not the most popular Coke product.
I would have to believe that this is some sort of marketing agreement between Coke and CO. Coke supplies free Zero???
Almost every time I fly, Coke Zero is available when I ask for it, but now I suppose I am just the only one asking for that one can put on by Chelsea.