It looks like the December bar (yellow) is actually for November if you take each bar as a month (which lines up with the rest of the marked points). The labeling on the graph is wrong (the yellow bar should be slightly below 10 billion and labeled as November). I'd like to see the downloads per month (and especially see the paid downloads per month), but as a marketing tool, I'd bet that 10 billion downloads sounds better than whatever their current downloads a day rate is.