If you've ever bought a house, you've probably seen a deed of sale for a chunk of real estate. Page after page of inscrutible legalese, complete with crossings-through and footnotes and sidenotes and whatever. When you sign your name in blood on the bottom of the last page against the signature of the vendor, it is generally taken as meaning that you “own” the house, but if you get into the small print it's a lot more complicated than that.
Ownership of a novel is like ownership of a house. I wrote “Accelerando” and I “own” the copyright on it, but I'm like a landlord who owns a plot of land, then sells the right to build on it and live in the building to someone else. Worse still: to several different folks on different continents at the same time. The “tenants” are publishers, who take the unformed land (the book) and turn it into something people enjoy using. And they like to sublet the property for money to other tenants — the reading public. They don't want squatters moving into the attic and setting up home without paying them — or worse, claiming to have owned the land all along.