Awesome to see you actually went into depth on my comment! So yes you just might be right about the stigma on admitting you have a depression. It would be lovely to get some Japanese perspective on this. I do have to mention again I am no expert on this but have recently traveled to Japan and tried to educate myself as much as possible on their culture and traditions.
Again, I was just speculating with these figures, would be cool though if there were some truth to it.