+1, DX11 is backwards compatible in the same way DX10.1 is, i.e. it's not.
Yes, I don't know where all this talk about ATI's SPs being more "general purpose" is coming from
If anything it's the opposite...
Unfortunately there is no guarantee that ATI's tesselator will be DX11 compliant. In fact, given NVIDIA's heavy involvement with DX11 I would bet against it