This isn't really true. I would venture a guess that Toni Morrison's college education had a pretty big impact on her future as a writer. But, there are also thousands of tremendous musicians, artists, writers, etc who can't make a living with their craft because the funding isn't there for it or the market isn't there for it. They either have to find jobs to supplement their income (often teaching), or they have to find day jobs that will support their craft.
Anyways, the point (as stated before) is that standardized tests only address a few types of intelligences, because society has placed greater value on those. Saying that a musician/artist, who might have stronger right brain intelligence doesn't need a college degree to succeed ignores the fact that right brain intelligence should also be a valued trait of businessmen.
No, it really is true. Art is independent of education. You can perfect your craft in a classroom setting, but you don't have to go to school to be a great artist, or a great singer, or a great... whatever.
Not every writer, singer, poet, artist, dancer, musician, etc. has gone to college. At the same time, not every successful businessman has gone to college, either. So there's not much point here, other than to say that some people have innate talents. The right school can perfect and enhance those talents, but not every school will, nor will every person truly benefit from school.
Still, I would encourage everyone to go to school and get a degree - more to conform to society than because I truly believe great knowledge comes from college only. It doesn't. It's just more concentrated there.