"North Korea has enough conventional artillery positioned on the DMZ, that they could annihilate Seoul and it's 20 million people within 10 minutes. That's why journalists use the 60 km term, because that's the range of conventional artillery"

Worst case scenario and not even close to what would realistically follow. Clearly you need to do some military research, it would be bad, but better bad now and confined to South Korea then actual nuclear threats to US, Japan, Canada... The thought that MAD (mutually assured destruction) will work with NK is painfully stupid. 

More countries with nukes make nuclear war only a matter of time. Furthermore, just like NK got its technology on blackmarket from Pakistan and/or Iran they'll soon be selling it and we'll end up one day with nations going nuclear left and right. If NK and Iran set the precedent others will follow. 

Eventually, a jihadi group buys a mobile nuke or dirty bomb and somewhere gets lit up that way too. Tick Tock Tick Tock