UPDATE - November 21, 2008: PC Games Hardware published a revised statement. Ben Basaric now confirmed DirectX 11 will be delivered with Windows 7. The site also speculates DirectX 11 may arrive for Windows Vista as part of Service Pack 2 for Vista.
Here's a snip from the original article:
PC Games Hardware had an interview with Microsoft Germany Product Marketing Manager Windows Ben Basaric about Windows 7. One of the things he revealed is that it's unlikely that DirectX 11 will arrive together with Windows 7:
PCGH: Will Windows 7 be delivered with DirectX 11?
Ben Basaric: That is to be determined yet. I could speculate, but that wouldn't help you. But I can give a tendency: unlikely.
PCGH: Will Vista drivers work on Windows 7?
Ben Basaric: Our aim is to make any program and driver that worked on Vista compatible to Windows 7. Therefore I can answer this question with Yes. There will always be the one or the other exception, but because of this we had switched the driver model with Vista.