http://www.stuff.co.nz/travel/asia/8020507/Airline-serves-KFC-for-Christmas I can't imagine having KFC on Christmas Day. Would make for a very quick and less messy meal...
You still do - this is just a option not the only choice and they are only serving it in the cheap seats, they have done other tie-ins in the past.
I actually enjoy KFC food, especially the mashed potatoes, which I'm sad to see won't be served on the flight. However, its high level of greasiness doesn't exactly agree with the digestive system most of the time, so I can't imagine having it on a flight with everyone else eating the same thing. My stomach hurts just thinking about it. As for it being a popular Christmas meal, I can see that. Kind of like the tradition among many families in the US to have Chinese food. Often your family will have the large together-meal on Christmas Eve, and then the last thing you want to do on Christmas is cook another meal, you want to play with your cool new things (or spend time with the family, I guess that's conceivable as well), so you order take-out.
It's a bizarre notion to me. Christmas Eve is nothing here. The main - and sometimes only - meal is Christmas Day, so having KFC then is just weird.