I don't know quite what you mean by volumetric grass-- I can tell you that, like the water, it looks 100% real. It looks as if each blade of grass was individually created and animated seperately. Theoretically, they could keep on perfecting the game forever and ever and ever, so they've got to stop sometime. I don't think that ending at the end of September is "early." Since they worked so long and hard, they all get a month off before coming back to work on "secret future projects.."
As for the Dolby 5.1 surround: I have also read that they have implemented it in, but I can't say officially because I didn't hear it from them directly while I was there.