I have tested it. Got Aspect Extraction maxed on 2 of my characters. They frequently receive kuta and rekuta.
I have 2 characters w/o Aspect Extraction and only hirelings 3/3. They aren't getting a single aspect rune.
So no, this is not rng. It's a bug. Not sure if it was "fixed" ZoS style or if it's getting fixed in 1.5?