F1 is a console port. It was designed and developed to run primarily on Xbox. Xbox just about constitutes DX9 (of sorts) but it can cope with high poly models, but it is not capable of the tessellation processing involved with true DX11 - it does not have the hardware.
As a side note, DirectX (9, 10, 10.1, 11) is a Microsoft product and therefore is in direct competition with Sony, who use OpenGL rather than DX hence you won't find DX anything on PS3.
With all that in mind, for F1 2011 sure CM (or developers in general) do tack on some other DX11 features at the end, like soft shadows, MLAA, SSAO and DOF (Depth Of Field control) etc which will make things look a bit prettier and obviously cost you FPS - they will never be true DX11 without making use of the tessellation processing unit offered on a DX11 card. To do that would involve bespoke development, more time, more money, more resources, and that's why you will never see true DX11 in a console port.
That's my understanding of the matter anyhow.