(looks like I lost this before sending. It's mostly old stuff at this point, given futher comments that already passed, but here it is)
If there were no copyright, nobody would have any bussiness in hiding source code, therefore nobody would hide it.
The business would be *exactly* in hiding source code. If I have the program, I can't [realistically] fix bugs or add features unless I have the source. So the software company would get the same proprietary advantages even if copying would be allowed.
Some ? What about music and films ? I think the situation is exactly opposite. With the exception of books, everything else has its source hidden.
Physically, you don't have the source of the book either. If you want to make a "derived" book, you'd need the source in order to only type in your changes (instead of all of it, plus dealing with layout). With music you don't have the score, and with films I can't tell what the "source" is. But I don't think it's importanto to detail what "source" is for the different types of work.
In all cases the user's perception of the authoral work is the whole of the work, there's nothing hidden. Even if you need to retype it all or rewrite the score in order to make a derived work, that's pretty easy to do. For films, you just need to produce the missing scenes to make your derived work. And the original author has no real direct advantage over other authors (beside details such as having the actors and the material used in the former film).
The difference with software is that the user's perception of the product is *not* everything the product has to offer; being able to copy and run a program isn't enough to make a modified copy. Or even to translate (while a film and a book is easily translated, here is music that is "technically" different).
Disclaimer: this one of "user perception" is not an idea of mine, I've read it, and it's poorly expressed mainly because of my English un-skills.
/alessandro