This is really unfortunate, but not surprising. Nikon's cancellation shows poor judgement, but their lack of explanation is pretty consistent to the way things are done here.
Generally speaking, the Japanese do not like to see themselves as anything but victims of WWII. A year or two ago I saw a photo exhibition at the Tokyo Metropolitan Museum of Photography that focused on the Japanese in Nanking in the 1930s -- it only had photos of military leaders, parades, and the Chinese welcoming them to their city. I think the Japanese generally don't admit to any wrong-doing, if they can get away with it (the government especially).