Is this plagiarism? (Update: jury says no)

When does the copyright expire? Or doesn't it?

I was thinking about something like this the other day. I love Eric Carmen's "All By Myself" as I love the Rachmaninoff concerto it's based on. Now, it was widely known even in 1975 that it was based on that but not realizing that the composer was so contemporary that he had only died in 1943, I had always assumed it was old enough for it to be in the public domain. But then I looked it up and discovered that Carmen did indeed have to settle that issue with the composer's estate.