Most artists agree that great art is a distillation. Say as much as possible, with a minimum of brushstrokes. Leave out as much detail as possible and still convey the whole picture.
So it seems a natural extension of that philosophy to use a minimal palette: to convey as much color as possible with as few colors as you can get away with.
A few years ago I was priveleged to see an exhibit of Wyeth's Helga pictures. He may have had an even smaller palette than you're using. I never once felt he should have used more.
Jeff,
Thanks very much for your very nice comment. It is true...we, as painters, have the prerogative to include or exclude; to eliminate or to add as each of our creative processes dictate. I
Wow, I hadn't ever seen this painting before. It's wonderful! I really, really like your composition. The gesture of her body language coupled with her position on the canvas is so perfect. I really enjoyed it - thanks for bumping it up so I could see it!