Dang, I can't find the link now, but I recently read an article which says that contrary to what people have been saying, DX10.1 will work on existing DX10 cards. If I find the link I'll post it.
I can't find the actual link I was thinking of, but if you search for "DX10.1 backwards compatible" it results in many pages suggesting that 10.1 is just a very minor update that will work with current DX10 cards