I agree.
The early dev kits probably just include the API's and documentation for the C/C++ programming interfaces. You don't need to know exactly what the hardware can do until you start optimizing, you just need an approximation so you can start coding. I believe the Play Stations use OpenGL or something close for their graphics API, and Nintendo has said that the Revolution will be using the same API as the Game Cube. The X-Box will no doubt be using DirectX. Point is, early dev kits don't need to exactly reproduce hardware performance, just the software interfaces.