Supersampling antialiasing, heard of it?
With DX10 and above, only the application controls antialiasing. That is why it is no longer possible to "enhance" antialiasing modes offered by the game with AMDs sparsed-grid SSAA or Nvidias ordered-grid SSAA (via the nHancer tool) or any other "special" mode.
But especially in modern titles, the image gets "unclean and shimmery" in certain areas due to shader aliasing - something that "normal" multisampling antialiasing (that is the only kind of AA offered in all current DX10+ games) cannot combat as it only works on polygon edges and not on textures or anything else for that matter. In DX9 one can get a near perfect clean image by using SSAA - which is not possible in DX10+ apps...seemingly until now.