This trend does pose some interesting questions:
Firstly, I take it these are sales figures of pre-built PC's. I wonder how the shipment and sales of individual PC components have fared against the rise of tablets. Consumers seems to be more keen on keeping their existing box and upgrading it to keep up than buying a brand new PC outright. With the money they save they can justify buying a tablet.
Secondly, can this global trend also have played some role in Valve moving to sell a Steam Machine? Surely they can see that their potential client base is moving away, slowly but surely, from traditional desktop PC's and onto either consoles and/or tablets. It would make sense.
Thirdly, how does laptop sales affect these figures? I didn't read any mention of laptop sales. And also how have these so-called Ultrabooks impacted the trend as well...