The difference between a real jazz ballad and a smooth "jazz" song?

Whoa, first off, you need to correct those people. The words smooth jazz and Coltrane should never be in the same sentence. Except for that one :D A jazz ballad is not really a genre like smooth jazz, its more a description of how a tune is played. Generally speaking (though I'm sure you'll be able to find an exception to anything I'm about to type) ballads are slower, softer in volume and generally sound more "spacey" as in the playing is more exposed because of the slower speed of activity (slow tempo) and generally the rhythm section plays with more space and less busy then other tunes like latin, medium-uptempo swing and such. Smooth jazz is a genre that in my honest opinion, has little to do with jazz and has a misleading name, but I'll save the smooth jazz bashing for another day. In smooth jazz, tempos vary and the rhythm section (drums, bass, guitar/piano) playing varies from somewhat soft acoustic rock to sort of R&B/funkish grooves. When you refer to ballad, you are generally refering to how you want to play the tune. For example: Musician A: I want to play "I Could Write A Book" Musician B: You want to take it as a ballad? Whereas the word "smooth jazz" generally isn't something too commonly used to describe how you'd want to play a tune.

ahah

The artists you mentioned weren't referred to as Smooth Jazz, But Cool Jazz. Big difference.