Korea has been partitioned for more than half a century. To refuse to recognize that fact is plain silly, that goes for South Korea and Japan too.
I'm not sure what you mean by recognition in this case. You seem to be conflating two distinct meanings. The US of course does recognize, in a de facto manner, that Pyongyang's goverment is in charge of North Korea and they hold it responsible for what goes on within its borders. I expect that maps of the world in the US are marked with a border through the peninsula with one side designated Republic of Korea and one side designated Democratic People's Republic of Korea (no doubt the ROK is decorated with flowers and the DPRK is decorated with skull and crossbones to help out Sarah Palin as well

)
So the US does not refuse to recognize that fact. What you seem to imply is that recognition of that fact leads, automatically, to full de jure diplomatic recognition and bilateral relations with embassies and American ambassadors swanning off to the Revolutionary Opera to watch Sea of Blood in some apparachik's Cuckoo.
You also say that failure to elide the two is childish or vengeful on the part of the US but this fails to appreciate that diplomatic recognition and the recognition of sovereignty of a state is not always a simple matter. You say that Japan and South Korea are also childish in their refusal to recognize the government of North Korea.
Well, a few things:
In a non-childish sense with-holding recognition of a country's government can be an important bargaining chip. In the case of a country like Japan, it still wants to see North Korea resolve, to its satisfaction, the issue of North Korea's abduction of Japanese citizens. Now, maybe North Korea will "play nice" if Japan recognizes but then again maybe it won't. Why does North Korea get an automatic privelege for potentially nothing in exchange. As it happens Japan already give North Korea plenty of food aid and receive Tae Po Dong missiles in return as they're fired overhead. This isn't the behaviour that Japan thinks is worth rewarding. Is it childish to refuse to indulge the petulant bad behaviour of others?
With South Korea and the US there are some difficult issues of the maritime border. South Korea claims the Northern-Limit-Line is the maritime border whereas the North claims the line should be drawn further south. This issue probably makes a formal peace treaty difficult.
By the way, technically Russia and Japan are still at war since the Soviet Union declared war on Japan and seized the north-east islands off Hokkaido and no formal peace treaty was ever signed.
As for diplomatic non-recognition, as you surely know the US doesn't recognize Taiwan (Republic of China) nor does almost anyone else even though everybody knows it is a sovereign independent country. Do you think the entire international community is childish? If so it hardly seems fair to single out the US. Pakistan refuses to recognize Jammu and Kashmir even though everybody knows it belongs to India. Similarly, your pals in Iran (I know, I am just being cheeky!

) refuse to recognize Israel even though it has been there for as long, if not longer, than North Korea. Pretty much the whole of the rest of the Middle East is the same and there Israel doesn't even appear on maps of the world.
I am not trying to change the subject with this I am merely showing that the non-recognition in a diplomatic sense between the US and North Korea is not as outlandish as you imply. I also think that it is a mistake to think that the default position for those who occupy a certain amount of land is recognition from everyone. If you think it is the default then it must be a principle applied universally. This can have knock-on problems. When the Taliban appeared in the south of Afghanistan, Pakistan said it would recognize the Taliban if they controlled X amount of the country. I forget which cities they were expected to control but they went on to fight wars of conquest against Herat and Mazar-i-Sharif and ended up with the recognition of a total of three countries - Pakistan, Saudi Arabia and the UAE.
Then the US goes on to break the agreements it made, because of Congressional opposition. Or because the new administration doesn't want to ratify it.
Well, this was bad I agree but you have to remember that in this case we are talking about a Clinton administration making promises and subsequently having its deal scuppered by a newly-elected Republican-controlled Congress who didn't want to fund a country that was still, with fairly good reason, on the state-terrorist list for blowing up a South Korean passenger plane with an onboard bomb and trying to assassinate the entire South Korean cabinet in Burma.
Unfortunately things don't run as smoothly in governments with a division of powers when compared to totalitarian regimes such as the DPRK. The Agreed Framework made bilateral recognition up to the Ambassadorial level a final step not an early step. Again, I don't have problem with asking your enemy to work for what it wants from you.
http://www.kedo.org/pdfs/AgreedFramework.pdf
An important thing about the framework is that Clinton aides did walk around saying that they expected North Korea to collapse any day soon anyway which may or may not have been some kind of assurance to the Republicans that it was worth making this deal but at the same time this was happening Kim Jong-il put North Korea on a war-footing with its Military First policy. And, of course, they repeatedly violated the framework deal and finally walked out of the NPT. Again, I don't see why it is the responsibility of the US to go running after Kim Jong-il and promise him goodies and again, I think that the petulance comes from North Korea.
Why would they do this? Why does North Korea scupper the peace plans? Are they, as Joey might say, insane? Isn't it really the US that's insane?
Well, no. North Korea is not insane and the US hasn't forced them to be nasty. The truth is that North Korea's regime can't survive without an external threat. It no longer has an economy to speak of so it can't claim that its regime will improve the lives of the North more than the government in the South. All it can do is show that it has something else that the South doesn't and that is a determination to protect the Korean race from the wicked Yankees. In this he has some intellectual weight from professors of linguistics at MIT -
[That's the theory according to B.R Myers anyway]
For this reason I would like to see what would happen if the US offered a peace treaty on a plate.
Every country in the world knows North Korea is a pain. That's no reason for the US to break its promises. Just don't promise anything that might be too costly.
The Korean war ended 58 years ago. Just give the North a peace treaty recognizing the status quo. What they do with it (wine or sign) is their problem.
Again, I think this is a conflation of two senses of "recognition". If some International Relations experts could help out though I'd be grateful.
Here's a kind-of thought experiment. What do you think the North would do if a peace treaty were offered? I think I know as according to the theory spelt out above the North would have to find a way of rejecting it and blaming it on the Yankees. I think they have already done this anyway.
But anyway, if South Korea met to sign a peace treaty with the North would the North agree to it?
The bolded part is the rootcause of much of the issue. The US government is scared to death of losing face. And that's stupid. Why would you care if Kim Jong-il says the US is grovelling? Nobody in the rest of the world is gonna take him seriously for it, and even if some do, it won't have any consequences.
North Koreans care. This is how Kim jong-il derives his legitimacy. It must be seen that he is constantly winning against the Yankees. This is why the North will risk war and try to disrupt things such as shelling an island or sinking a South Korean naval vessel. Being in conflict is useful for him. Without conflict his people would be asking why there is no food for themselves and why the Dear Leader can't give them what they want.
Consider cost-benefit. Diplomatic recognition of North Korea and a peace treaty is basically free for the US. So just give it to Kim. If it works out, great. If it doesn't, it didn't cost anything anyway. And either way, it will make a good impression with China.
Well, okay, I'd like to see it tried.