Naomi: you're right, of course, but most of the postings here have been of the "wow that's weird" variety, rather than explicit claims of communication with the dead. The thing is, I guess, that people don't like being baffled so they reach for an "explanation" of what they've seen or heard.
It seems to me, though, that a real explanation of any phenomenon must by definition locate that phenomenon within the bounds of what is already known. It seems silly, at best, to encounter something for which one can't think of a mundane "Oh, so that's how it was done" description and then to use one's own ignorance as justification for a leap of faith.
Of course, it can be more than silly; it can be dangerous. You can wind up believing all sorts of daft things and living your life in accordance with those beliefs.