The Inquirer thinks that this has to do with ATI and NVIDIA release timings for the "Fudo" R520 and NV50, and to Longhorn delays and DirectX 10/Next.
We learned that it will run faster on existing hardware and that it will contain the usual number of four games that will run faster on existing hardware then the lame 500 points on current high end Nvidia or ATI cards.Source: The Inquirer