Art is more powerful when it tells a story. Any person can look at a beautiful scene in real life. Anyone can paint that. It takes a special kind of artist to evoke an emotion through a painting. This is the kind of artwork that really makes a person think and it tells a story.
In the case of many artists, there are tragic circumstances that motivated them, and shaped them and their art. I'm not sure misfortune is a necessary ingredient in great art. I do think that people who pour out their pain through songs or words tend to elicit strong audience response.
I believe it's a cliche´that great art tells the story of "les miserables" (i.e. the poor, the wretched). Misfortune is relative--in real life, a jilted lover's experience is often hardly a blimp on the radar of his/her friends, for example. What makes great art, rather, is the artist's ability to extrapolate the human drama of everyday experiences onto the larger pathos with which audience members would resonate. So I think it's the humanity, fallibility, or just the recognizable depth of the characters, not their specific instances of bad luck, that draws reader identification.
When it comes to art, or any means of expression, tragedy and misfortune often resonate very powerfully with audiences. They are feelings that are consistent among human beings, no matter your sex, race or background. That being said, I do not believe that great art must come from such places of despair and darkness. Much of the great art in the world actually comes from joy and hope, and the recognition of the beauty in our world.