In addition, I once noticed that some gourmet "natural" bottled juice drinks had silica on the ingredients list, to give the appearance of having some sediment in the bottle.
Are you sure it isn't used for the opposite reason? Silicon Dioxide (silica) can be used as a suspending agent, so seems like it may have been added to prevent the natural sediment from collecting at the bottom.
If they wanted sediment, it would be cheaper to just add some of the actual fruit sediment they already have from earlier in the juicing process, rather than purchasing another ingredient.