As pointed out by others the floppy disk icon is embeded in peoples understanding of computer user interfaces as the standard visual representation of the act of saving something.
The use of the floppy disk icon is a reflection of the technology that was prevailent at the time and so represented something the average user could quickkly associate with the act of saving a file.
The fact that the action of saving is still visually represented by the floppy disk in spite of it's rapid demise in recent times demonstrates the strength of association between the icon and the act of saving a file. If one were to attempt tp change the icon one would need to choose an image which is
- Easily associatable with the act of saving as the floppy disk already is
- Likely to remain in use, or at least in recognition, long enough for a sufficiently high number of people to recognise it
While I do acknowlege that the floppy disk has certainly outlived it's usefulness as the primary storage media of choice, I don't see it's role as the save icon ending in the near future.
If the icon were to change I believe major OS and hardware vendors would need to support such a change, which I don't believe is likely as doing so would potentially alienate a large number of existing users