One of the metaphors we CONSTANTLY throw around in my MFA workshops is the infamous backpack of Frank Conroy. As readers--at least, as good readers--we expect that the author tells us things because they are important. Therefore, every detail we get (and this goes double for details that are set off in some way), we tuck away and carry around with us, and if we get to the top of the mountain and realize we've been dragging around a phonograph and the complete works of Dickens and the sword of Damocles or whatever else the author threw out us for no reason, we are tired and sore and annoyed. (This becomes much more apparent when you're in a class with someone who's like, "Character's left-handed? Does it matter? Backpack! It takes place in Chicago? Backpack! Her friend has a tattoo on his ear? It's a Chinese character? For the love of God, BACKPACK!!!).

JKR, I think, would not be enjoy herself.