Extremetech has a thorough review of the new ATI chip the RV670, in its R3870 form here. And it states this about DX10.1:
"A quick word about DirectX 10.1, which is coming to Vista users with Service Pack 1 early in 2008: While this is the first chip to support the new API standard, and AMD is likely to make a big deal about that, you shouldn't really get too excited. DX 10.1 makes some of the things that were optional in DX10 mandatory (like 32-bit texture filtering), and it adds a few new nice little wrinkles that could be of use to developers, but it's certainly not going to be "the next big thing." We don't expect many games to support DirectX 10.1 for awhile yet, and all the games that do will also support regular DX10. In most cases, you'll hardly be able to see any difference between them (the DX10.1 version might run slightly faster, or have a better anti-aliasing option, for example). It's a nice feather in AMD's cap to be the first to support it, but don't let it be a big factor in your buying decision"
Which is in agreement with the advice I have been giving for months, it is just another minor version rev of DX and no big deal.