TechReport has looked into the Assassin's Creed DX10.1 controversy and got in touch with the developer lead of Assassin's Creed to get to the source of it.

Quote: "We have been following a brewing controversy over the PC version of Assassin's Creed and its support for AMD Radeon graphics cards with DirectX 10.1 for some time now, and we were perplexed by some of the issues involved.
Fortunately, the tech lead for the Assassin's Creed development team was kind enough to answer our questions about the nature of the game's DX10.1 performance increases, what they mean for image quality, and what the future for DX10.1 support in the game might be."
Read the full report on TechReport.