In short the sales are down by some 10-11% and it's because of tablets.
Wow, a whole 10%? Shocking! And this is while Windows 8 has flopped in the market. Which means, to anyone with the capability to think beyond the short term, that PC gaming sales have only been MARGINALLY affected by Windows and PC desktop downturn. Or, in proper perspective, the absolute failure of Windows 8 to capture new market share has barely had any effect on PC sales and PC gaming. 14% of New PC sales over a period which was recorded in the from 2011 to mid 2012 and reported in MARCH of THIS YEAR.
In other words, this is marginal at worst and more importantly, OUT OF DATE and OUT OF CONTEXT reporting.
You know what else was happening in 2011 and 2012? The American Dollar was in the toilet. A 10% slump in LUXURY PRODUCT SALES in that sort of economy is actually indicative of the continued success of products which weren't affected more dramatically.