Hug,
The author of your 2nd quote demonstrates an extremely poor choice of words or the words are those of an uninformed individual or one with an agenda. "Brought on board" vs. "checked".... world of difference what?
In the US, as in the UK, EU and much of the rest of the world, firearms may ONLY be carried as checked baggage. In the US ammunition cannot be packed with the weapon and the weapon must be in a locked container carried in a hold inaccesible in flight. Carriage of ammunition is, as you say, in accordance with IATA regulations.
In the US firearms must be demonstrated to be unloaded prior to their being accepted as checked baggage. The unloaded weapon is then returned to it's container and locked in. This demonstration is carried out at check-in.
You seem particularly incensed that a rifle was displayed at the check-in for inspection. Are you saying that UK airlines do not inspect checked firearms to determine that they do not contain ammunition? That would certainly answer your question as to which system was more hijack-prone.
I totally concur with your comments regarding the passenger's irresponsibility in this case. Perhaps it's time for Parliments and Congresses to enact "Criminal Stupidity" statutes.