When I was growing up I also lived in a largely rural area served by Northern Spirit/Arriva Trains Northern (not that I'd have known that at the time!), where the norm was to buy tickets on the train - there were only two staffed stations locally. My local station there was (and still is) unstaffed.
I still think it's reasonable to presume that if there's an opportunity to buy before you board, that you should do so, and I don't think that should come as shock (why presume that things work the same everywhere??).
However I do agree that the level of seriousness - fines of upwards of £100, and criminal records - isn't obvious, or broadly known.
I think the bit that isn't known or widely understood is that intent is irrelevant and, should a guard / RPI / TOC feel like it they can take you to court if you're on a train without a ticket when there were facilties to purchase at your starting station, irrespective of your reason for not doing so.