Musically as far as I know ONLY melody lines are copyright protected. If someone can tell me this isn't true it will be the first time I've heard about it. Chord progressions and rhythms do not describe a song accurately enough to be copyright protected. In fact MANY songs have EXACTLY the same chord progression. I very much doubt that guitar tablature is protected by copyright. It probably comes down to whether the website being threatened can afford to protect themselves against litigation. Even if they can't that doesn't mean that they are liable, simply that they can't afford to try to protect their rights.
While I support protecting musicians' rights it's times like these that I detest the attitude of the music industry. They don't represent musicians just their own right to profit from musicians. They are just panicing that independant distribution of music on the Internet is eroding the business model that has supported them for far too many years and they are trying keep the last remnants of profit from disappearing. I can't feel sorry for them at all.
[This message has been edited by Nigel (edited 09-18-2006).]