Anecdotal, I know, but I was on a flight a few months ago where the wire for the hand held controller for the entertainment system had gotten so hot it burnt my hand. I'm not sure how far away the autoignition temperature of cotton is from the burn-my-hand-temperature, but I suppose it's possible that if it was cotton on that wire as opposed to my skin it may have caught fire. And while the wire delivering that content was non critical and probably on a seperate power network to the main systems of the plane, a fire on a plane is a fire on a plane regardless of which system caused it.