Oh, I think I have my answer in the following blurb: " Since liquid can be pipetted much more finely than powders can be moved, this allows a different volume of liquid to be pipetted to each powder location, based on the actual weight of the powder that was transferred".
This machine is not just a powder dispenser. That's the thing. Which requires an accurate measurement of powder transferred/dispensed. Which is obtained by a gravimetric method, not volumetric.