Yes, a silly little book, but wars have started over such a thing (e.g., Mein Kampf).
I think the greater issue is that this whole debate centers around Japan's desire to be a permanent member of the UN Security Council. In one of the speeches, the Japanese Ambassador stated that Japan is confident that it will/could/would/ play a significant role as a partner/key figure in the stability of the Asian region (I'm looking for his speech right now, so please bear with me for the paraphrase). China, HK, and S. Korea are pointing to the textbooks as an example of how the region cannot trust Japan to "do the right thing." They, of course, are escalating their fears by imagining what would happen if Japan does gain Membership. It could (theoretically) shift the balance of power (China and S. Korea's relatively recent rise in economic power threatens Japan's dominance in Asia) back squarely to Japan.