To be accurate, Commanche didn't have a true volumetric renderer, it was just raycasting a heightmap[1]; essentially just as much of a hollow shell as polygon rendering techniques. However, you are correct to point out that this tech is not particularly revolutionary; others such as the Atomontage engine[2] show voxels can be leveraged to create detailed, destructible organic environments.

[1] http://www.flipcode.com/archives/Realtime_Voxel_Landscape_En...

[2] http://www.youtube.com/watch?v=_CCZIBDt1uM