Is it really safe to assume D3D10_SDK_VERSION will always keep the same value? (I know d3dx9 does it as well.) For d3d9 the SDK version changed between d3d9b and d3d9c, for example.
At least with all d3dx10 DLLs released so far, D3D10_SDK_VERSION has not changed. Obviously, if it does change in the future, we will need to accommodate that in new DLLs.