While true, those statements do not lead to intuitive conclusions. For instance, building a nuclear weapon WITHOUT an initiator is FAR more difficult than building one WITH an initiator. The fact is counter-intuitive to the surface logic.
Moreover, getting a "chain reaction" is a fine way to generate heat and radioactivity, but it is a far cry from generating the super-criticality needed for an explosion.
Furthermore, simply trying to put more and more U-235 or Plutonium together in one mass will lead to a fizzle far more times than it will lead to an explosion due to the neutrons firing at the wrong time as the material comes toward close contact with each other. The technical hurdle involved with the precise timing of the necessary neutron emissions is a non-trivial endeavor, the solution to which is contained in the initiator/trigger.
And that's how you will find that EVERY nuclear weapon is made, with an initiator/trigger (and certainly how every small "backpack" nuke is made, as small size presents even more daunting technical hurdles).
Well, the radioactive materials (contained even in your own link that you posted onto this thread) inside initiators/triggers decay. Polonium's half-life (as posted above) is about 138 days, for instance.
But wait, there's still more: not only do the initiators have a finite life-span, but the electronics that are exposed to the radioactive materials inside the bomb likewise degrade.
Thus, even a FULLY WORKING, ARMED nuclear weapon requires frequent specialized maintenance. Without it, the weapon soon deteriorates into little more than a poisonous dirty bomb.
But the urban myth of the "hidden cold war nukes" makes for great tabloid journalism. What could be scarier than the thought that spies are selling atomic weapons that are already pre-positioned in our own back yards?! Quick, everybody run for the hills, the Sky is Falling!