Seems to me they are focused on use cases and problem areas than implementations, and 3d printing and drones are means to some end as you've also mentioned. A category for 3dprinting or drones could mislead founders to fetishize technology than to have the problem guide the solution.
But at the end of the day, it's still a16z list and subject to their interpretations.
But at the end of the day, it's still a16z list and subject to their interpretations.