Mike offers a good example here of non-abandonment of copyright. On
the Naxos site you can find several Met operas but they say in big print
"Not available in the United States". You can't get them from Amazon-US
either. You can from Amazon UK and there's nothing on Amazon UK saying
they won't ship them to the US, but I would guess that it's illegal to
do so.
If an American goes on Amazon UK and buys these and they ship them
to America, who's breaking the law, Amazon UK or the purchaser? Or is it
somehow legal?