I believe the trailer contains evidence of the snow having volume in the part of the sequence the OP was talking about. I've just re-watched around 50-53 seconds in, first at quarter speed, then at eighth speed. As the hero goes into his 'ready' stance on the edge of the cliff watch his right foot. it starts in full view; as he moves it back slightly it seems to sink into deeper snow, the result being that his right foot is half buried. It could be a clipping issue maybe. I'm no expert,
Also read over http://www.gamesas.com/index.php?/topic/1169809-the-famous-dynamic-snow/page__st__20__p__17239068#entry17239068 and see if you discern the things I describe. Especially at 2:15-2:19... how the snow pops into place in the mountain crevasses. I think it's just an LOD thing, the one that pops in is slightly more detailed. But I don't know if this is anolyzed in realtime, precomputed with some kind of voxel algorithm, or is simply a static part of the mountain meshes (and a part of the mountain LOD).
Take a look again at that section of video (0:50-0:53) ... His left foot is hovering in air (the shadow on the ground is clue)! It's certainly a foot placement issue. I was really hoping with Havok Behavior and Animation they'd use the Foot IK solver (the game takes note of the terrain and places the feet accordingly) ... So I'm pretty sure that's a clipping issue.