zubin is right. jazz musicians usually enrich the chord harmonically and so use more 7s 9s 13s. Look at it this way. 3 notes together sound nice dont they? The 1 3 5 harmony is nice so what if you add one or two or three more notes to it? Wont it give the sound a whole new dimension?
Also, as I was saying in another thread....once you start using major 7s etc you notice that most chords can be substituted with other chords or superimposed upon each other. Say the band is playing a C major chord. You can just play a G major triad and you'll get the notes C E G B D which make up the C major 9th chord. This is one of the simpler concepts though.
Hope that helps a bit.
And surely you’ll buy your pint cup !
and surely I’ll buy mine !
And we'll take a cup o’ kindness yet,
for auld lang syne.