Dirt 3 and F1 2010 Don't look as good as they should

it depends really on how the shadow is implemented, there are many ways of doing shadows, some really fast with low quality others are performance holes.
I am not into rendering, but take shadow mapping for example.

it is fast, but it has its graphical glitches and to make the image nicer the only way is to increase the size of the shadow maps. So you will have a shadow with more resolution but it will eat away your performance as the shader will have to work with much bigger textures

this was just an example.

your card has all the capabilities of dx11 specifications and when you code in dx11 you have to use those functions, so there is nothing missing.

Are the graphic settings the same in both SS's? It definitely looks like the textures in DiRT3 are choppier and much more flat. That could be one of many things, however, I would say the most plausible would simply be the graphics are turned down, or in making DiRT3, they sacrificed map size for performance.

DiRT 1 for the win

I dont know if you have resolved this or not, but just an update for AMD users: 11.5b hotfix apparently resolves some performance issues with Dirt3. Not sure if it will enhance the look though!

I wonder if tesselation is on AMD optimized or off instead of use application setting...