@MrsWinslow - Maybe the difference lies as much in how it's marketed and for what purpose it's intended. Maybe the difference between poetry and prose is sort of like the difference between erotica and pornography -- partly in the artist's intention, partly in the eye of the beholder, and partly determined by certain conventions. Poetry is usually more, well, poetic than prose, no matter what shape it's written in.
If you want a word that limits its meaning to traditional poetry, meaning that it has lines of a certain length and rhythm, you can use "verse." It's broader in some ways than "poetry" -- Shakespeare's plays were written in verse, but you wouldn't really call them poems -- but it is more narrow as far as the structure.