Of course you notice a lack of Ninjas. They are ninja's, you ain't going to see them less they want you to.
that said, Kusari ain't japanese. it's based on a japan from the 1800's, but that is all. After several thousand years any culture is going to diverge from it's root culture....
I honestly don't know. I'm not a ninja. I probably could be if I ever met one, but since I've never even seen one, it ultimately kinda throws a giant monkey-wrench into my ninja training.