"Hence you can not ask the author to get a spare cd."

That's not really the question. The question is, now that I have this scratched CD, why is it wrong for me to hop on a torrent and replace my scratched bits?

Obligation to produce a new CD would indeed require an actual contract, but "new CD" is not the same as "replacing my music".

The real problem this exposes is that the law has a concept of "source of the bits", such that "bits from your CD player" are different from "bits from a torrent you downloaded", even if they are otherwise identical. Standard reference to the "color of bits" essay: http://ansuz.sooke.bc.ca/lawpoli/colour/2004061001.php ... and I'll basically defer the rest of this comment to that essay since I doubt I can improve on it here.

Right. You don't need a license to protect your legal rights. You haven't asked all your friends to sign licenses promising not to rob you because theft is illegal. Record companies shouldn't ask people to sign agreements that they won't break the law. The law is already written. Why do you need a license on top of it? Licenses are for covering situations not covered by law or, more notably, for giving away permissions which would otherwise be covered by law. If you were going to allow one of your friends unrestricted access to your car, it would be a really good idea to give him a signed license agreement so he didn't get arrested for stealing it. If you don't want to allow your friends unrestricted access to your car, you don't have to do anything.

Copyright law doesn't care whether something is an original -- derivative works are also protected. Copyright protects creative works, however original, where creativity is defined by some semblance of originality (in content, arrangement, form, etc).

You can totally ask an author for a spare CD; however, he's not obliged to give you one.

Also, you are mixing up contract law (licenses) with copyright law ("default" law which applies in the absence of a license or certain licensing terms).