Let's say my Roman novel gets published. When that happens, I'll sign a contract and probably get an advance check (against potential royalties) and then a contractual payment-per-copy whenever the book is sold to someone. That's fair, right?
Let's say the publishing company decides to issue the book as an audio-CD. But because the audio-CD rights were never part of the original contract, I don't see a cent of it.
Then let's say the publishing company decides to upload the book onto the internet, and charges for downloading. But because the internet rights were never part of the original contract, I don't see a cent of that either.
And then let's say I'm not the only one this has happened to, and we all get together and ask to have our contracts renegotiated for our next book to include those peripheral publishing rights, and the publisher says "Y'know, the novels we've published this year are pretty crappy, so we're going to write this year off as a loss and publish nothing but diaries of people who have been dead for a hundred years. So, y'know, don't quit your day job."
Now suppose that was my day job.
It's not an exact analogy, but it explains why I'll be picketing with the strikers in front of Rockefeller Center this weekend.