It's interesting that you can give away your copyright to another entity (if it's a "work made for hire") but you can't give up your copyright completely to place a work irrevocably into the public domain.
What if I create a legal entity, have it hire me to make a work, and then dissolve the entity? (That's mostly rhetorical; I expect the answer, if it exists, is messy.)
There's a difference. You never owned the work to begin with in a work made for hire. Example: a New York Times reporter never owns the copyright to his articles--they are owned by the NY Times from the beginning. There is no transfer. The article is in a sense written "by" the Times.
But if I write an article and then sell all the rights to the Times later, I can claw it back in a few decades.
The arguments are over what happens when it's not so clear. Like what if the Times contracts with an independent freelancer specifically to write an article?
What if I create a legal entity, have it hire me to make a work, and then dissolve the entity? (That's mostly rhetorical; I expect the answer, if it exists, is messy.)
EDIT: answering my own question: http://en.wikipedia.org/wiki/Orphan_works