The "or higher" phrasing is likely for the ignorant. Letting them know it is safe to use higher octane fuel in the event they couldn't get the recommended octane.
My '15 Mazda3 2.0 liter automatic has a 13:1 compression ratio. It was designed to run on US-grade RUG, and that's all I feed it. I've never heard any signs of detonation "knock," and I consistently get higher-than-EPA fuel economy, so I've never been tempted to pay more for higher-cost premium.
...then these three videos are worth a watch. Yeah, you might not like the guy, but his info is spot on. Lots more info that's in line with these facts.