How are they doing the grass? Lots of triangles, or a dedicated grass renderer? A friend was telling about a guy he knows who wrote the power-line code for some race, suggesting my idea way back when of using an alternative line renderer is being implemented. Grass like this seems another good situation for non-mesh rendering with a fancy 2.5D particle renderer. Such an engine could be a good fit for Cell too.
5 minute mark, detaled look at grass tech