Gareth is right, copyright applies to any medium. However, "Coca Cola" and "Gucci" aren't copyright, they're trademarks. Copyright exists to protects content, trademarks exists to prevent consumers being deceived. So, I could happily print T-shirts saying "Coca cola is horrible", and the trademark owner could do nothing about it - I'm not using the word to sell a product that pretends to be Coca Cola, and not even a 'moron in a hurry' (http://en.wikipedia.org/wiki/A_moron_in_a_hurry) would think I was.
That's all beside the point here though, because neither copyright nor trademarks apply in this case. What does, are the 'anti-circumvention' provisions of the DMCA. These make it illegal, in the US at least, to develop, publicise or use tools for getting around DRM (or liberating your content).
These nastygrams aren't being sent on the basis that people who publish this number are breaking anyone's copyright, or misusing a trademark to sell a counterfeit product, but because they are revealing how to get around a rights management system.
That raises the question of whether the DMCA applies extra-territorially. IANAL, so I won't test that here (on a non-US site), but I'd be interested to know from someone who is.