What makes you assume sports games are down, when the OP is about the gaming industry as a whole?
Gamasutra lays the fault for this squarely on Nintendo's collapse in the market, as the Wii and DS bubbles burst, in addition to one of the best Novembers ever. MS enjoyed growth for the year and the PS3 just barely managed to grow a little bit YOY as well. This couldn't compete with the DS down 50% and the Wii down 40% in a trend that started a couple of years ago dragging down overall figures.
http://www.gamasutra.com/view/news/3...rs_of_2011.php