PAXBoy
The puny locks used on cases are actually of a lot of use. I would never go through some countries' airports without one. They do not prevent entry, they are too easily broken, however they do indicate that the luggage has been tampered with. They same applies to the lockable rucksack netting.
Of course this is much more likely to save you from drugs charges than a bomb: a typical trick in some far-Eastern and former-Soviet states is for someone to plant drugs in a person's checked luggage. This could be for one of two reasons. Either they wait for you to clear customs, unaware that you are a mule, then steal your luggage or else the customs are tipped off about you, and in the fuss as you are arrested their mule slips through. Either way in some countries you could be facing a long time in a nasty gaol.
Never let your baggage out of sight unless it is locked. If the lock is brocken, immediately inform some form of security personnel, before opening it! Say you are concerned about a bomb, this will get it dealt with at a higher level, involving more people than drugs, reducing the chances of anyone corrupt trying to pin something on you.
BJCC
Do you know if most of the imitation guns used in these 'tests' are plastic? If so then the reporters are faking the whole setup. There is only one gun that does not show up in a metal detector (a ceramic Glock), and that will show up on X-Ray so has to be carried on the person, so will easily be found on a search. It is an extremely expensive gun which is difficult to acquire. As far as I am aware it has never been implicated in a hijacking.