What, you really think kids have no idea what floppy disks are? Of course they do! They're young, not stupid. It's not as hard as you're making it sound.
Language is full of dead metaphor. Words and symbols have meaning because they have been given meaning; most of the associations might as well be arbitrary. Doesn't matter; humans are very good at recognizing these associations and deriving the intent.
Floppy disks have entirely disappeared from our daily lives except as an icon (and then largely only on Windows). A computer-savvy 18 year old that grew up on Macs could have entirely grown up without ever using a floppy disk and rarely if ever seeing the icon. I know adolescents that have never seen a floppy disk. Being unfamiliar with an obsolete media format doesn't make them stupid.
As for the rest of your comment, I'm not sure what you think I was trying to make sound difficult. I was arguing that it's entirely possible to replace the floppy disk with an arbitrary symbol, and it's just inertia (user training and a strange sacredness afforded this one random icon) that really keeps it around. I think assosciating a distinct symbol with an action is pretty damned easy, actually. (Designing a good symbol can be hard, though.)
One need not have ever personally used a floppy disk in order to recognize the symbol and pick up its meaning through cultural context; this is exactly how we learn to associate meanings with most of the symbols we use. We gain familiarity with all kinds of obsolete technologies throughout the course of an ordinary education, and easily recognize images of such devices whether or not we've ever seen one in real life - but beyond that, we learn to recognize all kinds of completely abstract symbols and use them as comfortably as words or numbers. There's nothing harmful about the fact that the "save" icon happens to look like an obsolete bit of storage media; the "save" symbol could have any shape, as long as it doesn't already represent something else.
Of course it's possible to pick a different symbol to represent the action of saving data to permanent storage: but why bother? We have a symbol, and it's as good as any other arbitrary symbol might be. Changing it would create confusion for no benefit, since it's ultimately the association of the symbol with the action that matters, and not the history of that symbol's origin.
Language is full of dead metaphor. Words and symbols have meaning because they have been given meaning; most of the associations might as well be arbitrary. Doesn't matter; humans are very good at recognizing these associations and deriving the intent.