I think we're getting worked into a lather for no real reason. The difference between the "song that tells a story" and other definitions is that the first, "a song that tells a story," is the technical definition within the academic field of folklore, while "a slow love song" is the most widely-accepted popular definition. It's unfortunate that these two definitions should be almost opposite, but it happens sometimes. (In the field of folklore, "myth" is a story that is religious and believed to be true, like the story of Jesus or that of Moses or that of Isis; in pop culture "myth" is a story that is secular and shown to be false, as in "that's just a myth," etc).

The folkloristic definition of "ballad" is based on what the word meant in rural districts where such songs were collected (on both sides of the Atlantic), but in the meantime the word was still being used in popular culture, and it eventually evolved into the Michael Bolton defintition. So there's no use denying that the word means both things, but we can choose to agree on which meaning we intend, and usually in folk circles we choose the folkloristic definition.

To be even more technical, the field of folklore recognizes that "telling a story" is not an absolute quality, and that songs therefore exist on a continuum between pure reporting of action and pure emotion. Ballads are ones where, in the words of one great scholar, "action presides over sentiment." The other songs would be various types of lyric songs, counting games, etc, etc. This means that what counts as a ballad is indeed a judgement call, expecially on some of the more overwrought broadside texts which have both action and copious sentiment. "Streets of Laredo" and its family ("Unfortunate Rake," etc) are recognized as ballads by some, lyric laments by others; and confusingly, individual texts of this song may be more ballad-like or more lyric-like than others. It's a messy world, and trying to divide up the real world of human expression into discrete genres is hard to do.

Sorry for the technical stuff folks, but I AM a trained folklorist! Gotta use that knowledge somewhere!