An interesting piece on the mechanics of publishing in that country. One of the oddities about bookstores there — this I can confirm from my own experiences with Japanese bookstores here, too — is the strange way many books are filed by publisher first, then author. The used bookstore (Book-Off) that I patronize is not like this, but I think that's only because they have no reason to return books.
Tove Jansson, BTW, is the creator of the "Moomin" series of books, which remain perennially popular in Japan the way Peanuts is in the States.
I should also note there's no discussion in the article of the issues involved in translating a work for the Japanese market, or finding a publisher for it. I imagine those things are in a class by themselves.