I think that they are confusing cause and effect. I think that people are more attracted to and appreciative and can relate to artistic material, whether it be music, painting, or writing that is emotionally intense. Someone who is suffering and then conveys that suffering through an artistic medium is more likely to be successful, but not because they suffer, but because suffering is what the public relates to and desires. Oftentimes when we look at art we see a reflection of ourself and are in ways able to releive some of our own suffering/issues vicariously through the artists own release of emotion that is represented in his/her art. But that being said, suffering is certainly not a requirement for being a successful artist. I'd say talent and creativity are more important than anything else.