Whilst Valve were there they displayed that they had implemented higher dynamic range into the engine. HDR will be available in the game to those that support its requirements, however it is not currently implemented in the benchmark. HDR needs the a higher range, and PS1.4 only has -8, 8 range which is probably not enough - the HDR effects also require float buffers which none of the current NVIDIA drivers support. There is also dramatic visual differences between HDR being enabled and disabled.
HDR is currently not in the benchmark mode because NVIDIA don't support float buffers at the moment and the benchmark was designed to render equally on all systems.