@Setanta,
It shows that, despite their protestations to the contrary, certain posters would rather live in a fool's paradise than contemplate what could have actually happened. Cuban missile crisis aside, it looks like all the times an explosion was likely were down to accidents. US, UK and the Soviets have all had their moments, and I bet the other nuclear powers have too.
When Obama said he wanted to reduce the world's stockpile of nuclear weapons he would have had some idea of the frequency of near accidents. None of us really know the true picture.