This Reader's Digest snippet from 2011 describes how candy makers stretched out the cocoa by adding air: "The price of cocoa is soaring, and candy makers are stretching ingredients by adding air. They say the chocolate is creamier, with fewer calories." Wonder if they're still doing it, and wonder if you can tell the difference when you put the bars in water?
Of course, some chocolate bars are made with lots of air bubbles, like the British aero bar. We floated one once, and had it spinning in nice circles.
Here's a Businessweek article with more info.