I think songs are a bit different to novels. Because of the format - having to incorporate rhyme an meter - songwriters are more often likely to put stuff in that doesn't neccessarily make sense but fits into the rhyme. I don't have any proper evidence for this, but I did used to know a musician and once asked him about the meaning of an ambiguous line in one of his songs (it could be interpreted in a coule of different ways) and he said that it could mean whichever one you wanted it to. I definitely got the vibe from him that he put it in because it rhymed and sounded good, without neccessarily having any particular meaning in mind for it.

I would say some songwriters would be more inclined towards that way of songwriting and others would definitely consider themselves storytellers and have a definite meaning for all their lyrics. Telling the difference is not always easy.