Works for me. Set it in my Skyrim.ini and not SkyrimPrefs.ini. Worked the first time I did it, so not entirely sure why you'd be having issues.
http://i.imgur.com/b4Mq6.jpg
http://i.imgur.com/ONCVj.jpg
That looks more like applied Nvidia SSAO. I've tried getting grass shadows using the 3 mentioned commands under display and general of the skyrimprefs and skyrim ini's but it doesn't work.
Yep, those are definitely SSAO shadows, not what you're looking for. I'm having the same
issue (if it is an issue that is, not sure), though there is some grass-like vegetation that does receive shadows but just not the ordinary grass. I'm not sure if it's always been like this, I must've never noticed before. Haven't been able to find a solution for this.
Another thing I noticed is that large mountains, like whatiksname peak doesn't really cast a shadow. I mean it does, but just not a shadow as large as it should.