That is what we have found with the World's Best and poo smell. Luckily the cats seem to agree, as they use the WB tray only for peeing! We were hoping to get rid of the clay, as we don't like the dust from it and it cannot be good for the cats, but the cats do not seem to want that to happen (plus the Fresh Step clay really does hold down the poo smell best).
If I recall correctly, the Yesterday's News works exactly the opposite to clumping litter: pee causes it to disintegrate and you are supposed to sift out the used stuff then (i.e., discard the powdery, used part).