Floppy is a good icon because it's so readily recognized, even to those that have never seen a real live floppy in person, that it can be in fairly low resolution with only a little icon and still be immediately understood.
Other icons I've seen involve thick downward pointing arrows, usually of the green variety. Apple's firmware updaters are a good example. They usually have a chip below them. But for file saves I've seen a hard drive below the arrow on several occasions. Rarely you also see a globe above the arrow if it's an internet download.
But hard drives are not quite as recognizable, especially to the lay man, and don't fair well at low resolution/size.
The eye seems to accept progression from top to bottom better than left to right, and I think that's why this arrow method is more common than say an arrow pointing to a floppy to its right.
Apple's installer uses a grey arrow to a hard drive. In terminal:
osascript -e "tell application \"Preview\" to open \"/System/Library/CoreServices/Installer.app/Contents/Resources/Installer.icns\""
Installer.icns\""
You can see when you get down to the 32x32 icon the hard drive turns into a somewhat unidentifiable silver block. Now imagine that with a hole in the middle, a shutter, and a label. Much easier to identify.