If you would read and do searches this has been talked about a lot before. It is not true dx10 it allows dx10 only games to be played on xp.
"These compatibility libraries allow the use of DirectX 10 games on platforms other than Windows Vista , and increase hardware compatibility even on Vista, by compiling Geometry Shaders down to native machine code for execution where hardware isn’t capable of running it. No reason for gamer to change or upgrade the OS and video card(s) to play the latest games."