Supernatural does seem to have decided that its target audience is specifically fandom, rather than just casual fans. On the one hand, I think that's quite cool, but on the other it didn't start out like that (unlike, say, Torchwood, which I'd say is also very fandom-aimed), so, yes, I think a lot of people who've watched it from the beginning and aren't involved in fandom are just going to be very confused.