Headwinds can be more than a breeze. Check our this recent thread:
http://www.pprune.org/passengers-slf...don-track.html
This is all about the effect of headwinds on the speed of the a/c. Just the same when you are in a car on the motorway, except that the headwind might be 100mph or (as I understand it) even more. That means more drive needed by the engines to fight it and that takes fuel. Somewhere around the world, this is an everyday occurrence.