If you think about it, mail has no "modern" representation either and is still represented by a paper letter.
(image from "It's Time to Change that Metaphor")
As mentioned in the blog entry "The end of an icon"
It’s dangerous to base a visual analogy on a moving target. Technology will change. What’s clear and obvious today won’t be in 10 years; so what’s nebulous today will be totally obscure in 10 years. The problem with the floppy icon (beyond the iffy analogy) is the generation gap.
Still, as long as the underlying action is clear, that icon will survive.
(image found in many places, including in this blog post)