Uh... you know the concept of a shinigami wasn't present in Shinto/Buddhist/Confucian lore until Christianity wandered over to the East side and introduced a grim reaper to a new and unwitting population right?
Besides, there was a show on rabroadO for a while called Dead Like Me which is a similar concept. And there's something called Reapers that's airing now last I knew. Again, death, ghosts, people crossing over. Not to mention there was Touched by an Angel, which IIRC, had a lot of "we have to help this ghost cross over" type stuff. Oh, and then there's Supernatural, the X-Files, I think Joan of Arcadia wandered into Bleach territory from time to time, Ghost Busters....
Face it, the first chunk of Bleach (pre-Soul Society) is a fairly standard paranormal shounen battle manga. Once ya get into the Soul Society arc and beyond, it's a fantasy battle manga with some political intrigue.
Bleach isn't ABOUT Shinto or Buddhist ideals, it's just there kind of as a base mythology. And Kubo borrows from a lot more than that anyway. Americans are dense, but they know fantasy when they see it, even if the beastiary and arsenal of superstitions and spells are different.