Here's something I've noticed many times in music. The editors who put the chords on a song seem to think they are doing music theory rather than giving instructions to the accompanist (acc for short).

To take a simple example, supposed a measure has the notes ACE and G in it. The editor writes "Am7." But actually, if the acc plays Am7, it's extra work and may be too harsh. We can have the acc just do the Am chord and let the singer sing the G. When you put it together, all the harmony Am7 is there. This can give the singer the chance to add expression or to make the dissonant note special in her own way.

Here's a video of Ella Fitzgerald doing this song:

http://www.youtube.com/watch?v=wN2bkQMs4Zw

I don't think the acc is doing any of those fancy chords. The violins, etc, don't sound jazzy, they sound smooth and pretty. They are letting Ella do all the bluesy half-steps and are not overwhelming her line. (This is in the second half of the song.)
At one point the trumpet shows off, but it's while she is ending a line.

2. And then there are the editors who see the notes A C E and F# and say "I don't know what the heck that is! I'll just say Am7." The result is pretty awful as the F# in the melody crashes head-on into the G of the Am7 chord. This is definitely a time for the acc to stick with Am and for the lead to have the F# all to herself.

(I have seen editors put D7 on a measure with D F# A B in it.)

The environment makes a difference. Dissonance which is okay in a football stadium can be too, too much in a living room with a wood floor.