If history were like baseball, I could tell you whether this was "unprecedented" or "rare" or "something that is statistically pretty normal." Baseball statisticians are incredibly adept and have immense quantities of nice, neat data at their fingertips. I do envy them.
Anyway, two major powers have both issued pretty heartfelt apologies for military errors: China, for a submarine incursion into Japanese waters, and Israel, for killing three Egyptian policemen. Apologies are rare enough in the world. It's nice to see even pretty hardened regimes have the capacity.
No, I don't think this is going to be a streak, or a trend, anymore than the triple-play is a common occurence on the diamond.