I think you nailed it. From my own experience living there, I saw a lot of this with my own eyes. I remember a time when I worked in a restaurant (and taught English in the daytime) that had just opened a few months before I started, and me being the gaijin got every sunday off, but the kitchen full time staff to my surprise had been working everyday since opening without even one day off! We were all on salary, paid monthly of course.