Well, and Pro also for users with large demand for render capabilities, (RenderQueue, 64 bits render engine), people needing the Colada interface or interface with Maya etc., or wanting more control over or postprocess capabilties for their rendered results (gamma control, HDRI and PSD-layers format output)

See the compare table at http://poser.smithmicro.com/comingsoon/

My personal favourite is the exponential tone mapping. It prevents 'washing out' of light spots and gives a much more balanced image.