Currently, the environment ground plane is excluded from the ambient occlusion calcualtion. You can create a pllane under your model to create accurate shadows, but then you lose features like ground reflections in your screen grabs.
When computing AO, there could be chackbox that says "Include Ground Plane" which would create acurate shadows for rendering.
Alterantively, a "ground plane shader type" could be included so that you can have multiple ground planes with pre-rendered shadows in the scene (for differnt models or product configurations within a stage).
