A drop of water compared to the volume of Earth's oceans is about one part in 2^84, so your analogy is a bit of an exaggeration, as there are only 2^64 /64s to be handed out. Still, there are plenty of allotment sizes larger than /128 that are still not scarce enough to bother charging for unless you have some other leverage (lock-in or a unique advantage on some related product).