>Given that, at peak times, some commuter services run once every ten minutes, and thus are ~always on time per this definition, it's wise to be a bit skeptical of the punctuality reporting.

I think that makes sense. If a commuter train leaves every 10 minutes, but due to some technical problems, the first train of the early morning leaves 20 minutes late which then continues through the day, does that mean every train is late? The users wouldn't know the trains they're using should have actually ran 20 minutes ago, they just know a train is to go every 10 minutes.