How much of Japan's population syndrome is directly assignable to Japan's unique policies, versus the nature of first world countries in general?

Japan's population has been essentially flat for the last 6 years: 127,773,000 in 2005, 127,817,000 in 2011. It is headed south as long as the birth rate remains so low. So no question that the rest of the world needs to understand the effects of negative population growth. A decreasing population will test many economic policies that relied on monotonically increasing population to be effective. I doubt we can predict all of the policies that will break.