Icons are becoming dead metaphors, which is fine. We pick concrete concepts to represent abstract processes and eventually the concrete concept becomes obsolete. This is exactly what happens with language -- should we stop using the word "deadline" because we've forgotten what it used to mean before it became a metaphor for a due date?
I agree completely. Just because the original uses have stopped being so common doesn't mean the icons are bad now. In language terms, you could compare this to street names - very few people would know why the street they live on is named that way - its just useful that it has a name so people can find it.