Leeneia, Creative Commones isn't for "creative work which nobody wants to bother to copyright". On the contrary, to use CC you have to own the copyright. CC offers a way for you to manage that copyright, to licence others to freely use your work without infringing your copyright, and allows you control over how and where that applies.

Where music is concerned, the position is possibly muddled by the involvement of performing rights organisations, who take over the management of copyright on their members' behalf. I don't know how performing rights organisations in the US operate, but in the UK the PRS allows its members to apply CC to their works. You have to complete a form to indicate to which works registered with them this applies.

In mg's situation CC would allow anyone to use their work freely, but would still protect their rights should Nike want it for a commercial.