So, I hate to be realistic, but I don't think the way the GI information has been conveyed and perceived is really anything like reality, and has in fact gotten quite out of hand. I don't expect to be able to trudge through knee-deep snow, but I would sure like to. I imagine instead we will get at most decals on the ground which make it appear we've left our footprints in the snow, but this is simply a normal-mapped 2D texture.
I'd say you're probably right on that, obviously, individual snow-flakes aren't going to actually accumulate, but through use of some graphical tricks, I'd imagine one could create a pretty good looking illusion, which is likely what we're getting here. It sounds much more impressive if you make it sound like you have actual physically simulated snow, though, which may be why it's put in a way that led people to think that.