Remember that these numbers are "units sold". One octo core Mac Pro with everything you could dream off = 1 sale. One Netbook with a tiny screen for $299 = 1 sale. These numbers are of no real interest to the companies. It would be much more interesting to compare revenue. According to some recent studies conducted and heavily advertised by Microsoft, Apple actually makes much more revenue per unit sold than everyone else. So if we had a chart showing "million dollars" instead of "thousand units", Apple would look a lot better. But what a company really looks for is profit. You might find Apple to be number one.
Many years ago, there were the "Cola wars". Coca Cola and Pepsi Cola fighting it out. At some point the Pepsi guys figured out that Coca Cola marketing was counting "bottles sold", whereas Pepsi was counting "ounces sold". So they shifted their strategy to increase sales of larger bottles. The advantage: Coca Cola _believed_ they were in the lead and increasing their lead, when actually the opposite was true. Pepsi sold fewer bottles, but they had more revenue. Coca Cola worked very hard to improve their numbers, but they worked hard to improve the wrong numbers.