Some relevant quotes from podcast:
[Dec 21, 2009]
Why are there not etheric versions of the wall turrets when all the other robots turn to crazy etheric stuff?
A: There's actually a very good reason for that which I'm not going to tell you directly. There's a couple hints in the game and other even weirder places. Some of which you've found, some you haven't, some you probably don't realize is a hint. But yeah. The fact that things are robotic tends to make them not show up in the ether, there's an entirely separate phenomena that makes them be replaced in the ether.
[Feb 18, 2010]
Q: The Drone Signatures appear to have been cracked! …Have we found everything relating to those?
A: Um, [checks] [hehehe], let's see. Uh, there is an interesting note of sort that no one has seen, some mechanics that haven't been spaded out, and of course the actual story mysteries that don't have valid answers yet, though you don't have all the clues that are in the game yet to make that anything other than guesswork. But most of the relevant stuff is there.