Dx is not as programmable as OGL. Once you start an executable in a certain Dx level, you can't switch back and forward between 9 and 11 or mix them together. So it's either using dumbed down Dx11 or not using it at all - there's no middle option.
erm, no. just about the entire fixed function pipeline is gone since DX10, everything is based off programmable shaders now. OGL is the one that has been playing catch up.
and there's really nothing stopping you from from flipping back and forth from 11 to 9 besides the extra work. DX11 can work on DX9 hardware for that matter, so it can all be under one API.