There is a post going on right now about a quilt made with red & white fabric that, you guessed it, the fabrics were not pre-washed and the red bleeds like a stuck pig! Even though it was washed with "8" color catchers!
Here are a couple of interesting articles that address this issue.
this is my fave article.
http://www.textiletraditions.com/res...bric.htm#bleed
this is more for clothing, but store bought fabric falls into the same category really.
http://www.howtocleanstuff.net/how-t...from-clothing/