Steve Jobs famously proclaimed the beginning of the post PC era in 2010 at the All Things Digital's conference. It has taken more than three years for the industry and the analysts to start acknowledging this fact and the 'uncomfortable' truth. The iPad has always had an identity crisis when trying to classify it, while it preceded the iPhone in inception, it was released three years after the iPhone and it has more functionality than an iPhone and less than a laptop. So is it a mobile device or a laptop and answer has been that it is in between. Hence it was not included in the PC surveys and analysis. Unfortunately since Apple was pretty much the inventor of the 'modern' tablet, a tablet market share analysis was not the norm before iPad. So iPads were literally in a league of their own.
But more recently more traction on including them in the PC class has increased and I think most of the credit for this should go to Microsoft and Windows 8 for trying to merge the refrigerator and the toaster and failing miserably. Either way, even from the year of the iPad's release, some analysts have included the iPad sales in the PC sales and have claimed that Apple leads in the PC & post PC market share and this study further strengthens this claim. The decline in the last quarter can be attribute to a couple of things like a lack of new iPad model, thanks to Apple's new 'ship when ready' strategy and not follow fixed release cycles to combat competitors from taking advantage of knowing in advance, Apple's product release timings and also the complex channel inventory issue that Tim Cook tried to explain in the recent earnings call. The bottom line is that, this fall (2013) will truly assert or dismiss the notion of Apple's hold on the PC and post PC market for sure.