This is crap. It's also not very Japanese... the assertion that your apartment already has all the organizational equipment you need is utter bullshit if you've ever visited or lived in an apartment in Tokyo (that costs less than 5k USD a month). Even in less crowded places, there's usually a practical need for extra shelving, hanging space, etc. in order to keep enough clothes and related items around unless you live alone and lead a rather spartan lifestyle. I'm currently managing it, but only barely, and with a bare minimum of... everything.
It doesn't help that consumption here is positively rampant. Without making a value judgement, I'll just leave it here that shopping is a major form of entertainment.
This is the same kind of self-improvement crap that sells so well in the US. Don't make the mistake of thinking Japan doesn't have it too.
So, really, the only objection I have here is the idea that it's a "Japanese art." That's marketing; effective marketing, but like most effective marketing, it's a lie. I got rid of most of my stuff to move here, which was actually one of my goals, and I'm very pleased with it; however, the "joy" tenet is misguided, and the general lack of space in Japan has NOT inspired minimalism. It's inspired clutter and the avoidance of the home as a place to entertain and relax.
Again: Not a value judgment. Just observations from an American living in Japan and surrounded by the culture and people this piece misrepresents.