From reading previous answers to this question by Ron and other musicians, I think it's something like this:
In Japan, they charge much more for CDs than a free market would be able to get away with, so in order to get people to buy CDs locally (instead of waiting and importing from overseas for cheaper), they do heavy promotion of new releases. But, in order to dissuade importing, they require to be able to release the CD before other markets, and they require some sort of bonus material.
That may not be 100% accurate, but that was what I got from what I've read.