I think it really just depends on the fabric. I've had some fabrics that I purchased that are labeled "do not pre-wash". Others I've been glad I did because there was a noticeable amount of shrinkage.
The other issue you have to think about is that there are those very rare fabrics that will bleed the first time you wash them -- so just be sure that when you launder the finished quilt that you wash it on cold & if you have a lot of intense colors maybe toss in 1 or 2 of those Shout Color Catchers.