Is Creative Commons marketing pixie dust? Does it really do anything for musicians?
On big centralized content repositories, it does have concrete value. Publishers who need non-infringing music will go to trusted distribution points like Soundcloud, Freesound, Jamendo, CC Mixter, and Free Music Archive. These sites have standardized license terms, so that potential users don't have to read a new contract for each potential item.
Those publishers were sophisticated enough to understand CC terms. They weren’t going to do a general web search for any old flotsam in proximity to a CC license, though - it’s important that Flickr and Soundcloud are centralized.