Ah, thanks all. (Didn't consider Rocket Defense/Power Armor as it's not researched in my current game)

And yes, I assumed it was an oversight. Since refineries are placed rather rarely it probably won't matter much, though.

I noticed that the Oil Refinery seems to be the only item in vanilla that needs 5 resources to be constructed. This means it cannot but automated. Not that it's very useful to automate refineries but I was wondering if there was a specific reason for it.