So what about those North Koreans? As the SWJ put it, a small war in Korea was postponed. I'd query "small", especially in the special sense they use it - it wouldn't have been particularly small and it would have been defined by high-intensity battle - but perhaps they are really thinking of whatever would happen after North Korea, as in David Maxwell's paper I linked to. (Maxwell turns up in the comments thread.) The postwar is reasonably certain to show up; the big question is whether Korea has to go through the big war to get there.
It's worth noting that the North Koreans took care to be seen to be alert and causing trouble during the exercises off Yeonpyeong, but without doing anything that would be unambiguously hostile. It's also interesting that they seem to have used electronic warfare as a way of signalling their continued determination to fight in a field that wasn't a direct challenge to the South Koreans and their allies.
Actually, all parties to the conflict attempted to find alternative forms of confrontation in order to exert power while trying to keep control of the escalation dynamic. I recently saw somewhere on the Web a reference to the idea that having multiple independent forms of power or status was an egalitarian force in society as they could balance each other. It's certainly an important concept in international politics. North Korea's original bombardment of Yeonpyeong was a direct and physical, kinetic, attack on the disputed border - at one level, they hoped that if there was no response from the South, they would have set a precedent that South Korea could not treat the island and part of the surrounding sea as entirely its own territory. More strategically, it was a demonstration that they were willing to cause trouble in order to extract concessions, and that they were willing to escalate significantly.
From the Southern side, there were serious restrictions to the possible response. Anything they could do in the same context would either have involved risking bringing about the big war, or else risking a disastrous fiasco - a major raid over the border would have been too much, a commando operation to destroy the guns facing Yeonpyeong would have risked ending up with prisoners in North Korea. There is not much at the moment they could do to put pressure on North Korea economically, and the North Koreans often respond to economic problems by provocations designed to get economic concessions. The North Koreans held escalation dominance - they could choose whether to go further, without necessarily having to go for the ultimate deterrent.
This is why the navies were so important. Although they were constrained in what they could do in one context, the Peninsula, the US Navy and its allies were not so constrained in bringing ships into international waters in the area. The response was to move the focus of the conflict into a different context. Also, cooperating at sea allowed Japan and South Korea to demonstrate alliance unity in a way that they could not otherwise - nobody would bring Japanese troops to Korea, for example, but there is no such objection to Japanese, US, and South Korean ships (or aircraft) cooperating. This is still true even though the US-made or US-inspired equipment aboard those ships permits them to cooperate very closely indeed, with radars aboard one ship, aircraft from another, a command centre in yet another, and missiles aboard a fourth being internetworked.
Also, there was very little the North Koreans could do about it without taking unacceptable risks (even for them). The biggest concern for the allied ships was that the North might lay mines in the narrow seas west of Korea. Paradoxically, the North Koreans were probably self-deterred from doing this - had they got lucky and sunk the Jimmy Carter while she was spying around Yeonpyeong, the consequences would probably not have been ideal from their point of view.
Another parallel form of conflict was the nuclear issue. North Korea had just revealed its new uranium enrichment cascade when it started shelling Yeonpyeong, after all. Bill Richardson's officially-unofficial mission to North Korea brought back the offer to sell North Korea's stock of plutonium to the South. This sounds better than it is, precisely because they now have the capability to use uranium rather than plutonium. On the other hand, accepting it is sensible - it's a matching concession to de-escalate the situation, less plutonium in North Korea is probably desirable, and it moves the nuclear debate onto the slower "enrichment track".
The nuclear debate also provided an opportunity for the Chinese government to play the role of turning up late but bringing a solution. If the 12,000 rods do leave North Korea, a big question is where they would go. The Chinese might buy them and might even offer fuel of some description in return, a replay of the 1994 framework agreement.