Not only that. We appear to be far better at learning the meaning of new unknown symbols than one would expect.

Anecdotal evidence: when I first encountered a floppy icon, its purpose wasn't obvious to me at all, despite I've already used a floppy before. See the Chinese writing example in this thread as well. Apparently, prior knowledge of the real-world object doesn't affect usability as much as other visual features of an icon.

This makes me believe that, in future,

1) younger generations won't have any trouble with icons that represent old things they'll never see;

2) icon design business is going to profit.