Normal copyright gives an author a "bundle of rights" that they may license how they want or declare to be in the public domain. Even if you classify the GPL as "copyleft, not copyright" or "legal judo," I don't think it works opposite of the way that normal copyright does. In a world where everything was public domain it would still be possible to circumvent GPL's source code distribution provisions.
There is one part of copyright that might run counter to the GPL, however, and that is the right of an author to reclaim copyright after 35 years. If the right applies (i.e. not a work legally classed as work for hire) it cannot be revoked, even by the author, until the 35 year term is nearly over. This right is generally a good thing, but might be a bit messy or disruptive if someone who wrote old UNIX IP decides to try to reclaim their work.
Unfortunate or not, intellectual property is a term of art at this point. However, connotation can differ from denotation, and it often does in law.