You're assigning logic to the NK leadership.
"Logic" says you don't set off nukes and fire rockets at the USA, doesn't it?
I'm not sure NK is the most logical bunch.
Engaging in rational analysis (assuming some modicum of rationality on the part of other actors) is probably built into our mind/brains -- it's unavoidable. And anyway, doing so for the NK regime provides pretty satisfying explanations of its behavior, so I think that the onus is on those claiming that the regime is really acting irrationally this time to give us reasons to believe that this is the case.
After OIF in 2003, a compelling logic presented itself to the remaining "Axis of Evil" powers: unless you develop a credible WMD program as deterrent, the US will invade and topple your regime as it did Saddam's. NK did as such. So far, so logical. There's also a consistent history of aggressive maneuvers to placate local factions within the regime and to leech more resources from the world community either in the form of loosened sanctions or more aid. There's certainly no positive bargaining chip NK can offer consistent with their ideology, so they utilize a negative one. And its worked well enough for this and previous NK regimes -- again, logical enough.
Looking at the other side of the Pacific: the USG will have acted rationally if it estimates the cost of a nuclear strike on the West Coast (or some other genuinely aggressive NK action) and weighs this against the likely cost of a preventive (preemptive, whatever) operation to remove the regime. Since the probability of the aggressive NK action is so low -- at least if what I said above is right -- even if the nuclear strike would be extremely costly, it still makes sense not to launch the preventive operation. (E.g., if a nuclear bomb going off would cost the US economy $1 trillion and has, say, a 10% chance of occurring, then a preventive operation would have to cost less than $100 billion to be more rational -- pretty unlikely).
In short, it seems that either contestant's current behavior is approximately rational.
Additionally, since the nation is ranked #1 as the most controlled nation on earth - we're not exactly sneaking in spies nonstop to see what they're building and where. They're poor. They need money. How much would Al-quida pay for a nuke? We have hundreds of people coming across the border daily. They could deliver it without a rocket.
Don't you think NK being a potential threat to non-proliferation is a somewhat different subject than the current one?