I'm not entirely familiar with the feature set introduced by DX10/11 class hardware. I'm vaguely familiar with the new stages added to the programmable graphics pipeline, such as the geometry shader, the compute shader, and the new tesselation stages. I don't see how any of these make much of a difference for a 2D game though.

Is there any compelling reason to make the switch to DX10/11 (or the OpenGL equivalents) for a 2D game, or would it be wiser to stick with DX9 considering that that a significant share of the market still runs on older technologies (e.g. the February 2012 Steam surveys lists around 17% of users as still using Windows XP)?