The two Koreas came closer today than ever before holding high-level talks, setting a July 27 date for a summit. The presidents of the two countries are scheduled to come face-to-face in the communist capital, Pyongyang, the first such meeting in the 49 years since the Korean Peninsula was divided. Why should Americans care? A meeting between the two could cool Cold-War tensions and help further defuse a U.S.-North Korea standoff over Pyongyang's nuclear-weapons program. Already, though, signs are emerging of potential irritation between the two Koreas: the North refuses to discuss a second confab, which the Southerners hope to hold in Seoul. Longtime Korea watchers warn that hopeful signs of impending summits have been dashed before.