How can video companies use copyrighted music in projects?

As I understand it when you purchase the CD you purchase the right to use the music for personal use. So you can put a song you bought on a photomontage to show to your family of pictures you took. In these cases the person owning the copyright is getting royalties as defined in the agreement when they sell the record, CD or digital file of the song to you for use. You could not use it for a movie you charged admission to or montage you used for advertising or other commercial reasons without additional permission of the person holding the copyright.