Perhaps it is something to do with a lack of true DirectX11 style threading within drivers from ATi and nVidia?!?
A few developers have expressed their concerns over this, the good news is nVidia's upcoming CUDA 4.0RC driver HAS major enhancements

Share GPUs across multiple threads
Use all GPUs in the system concurrently from a single host thread
No-copy pinning of system memory, a faster alternative to cudaMallocHost()
Layered Textures for working with same size/format textures at larger sizes and higher performance
Faster Multi-GPU Programming
Perhaps this is what Crytek are waiting for? The DirectX11 path may already be coded, and in theory ship with the game, just the vital .exe is missing and that is because the drivers are currently not ready.... yet.
?!?

Either way I am still disappointed at this, even the lack of DirectX10!!

I am not quite so sure zanzabar, to me Crysis DirectX10 looks a lot better than Crysis DirectX9!
John