I don't pre-wash anything unless it's for a swap in which pre-washing is specified.
I like the feel of the fabric when it's still got the mill sizing in it, and I like how it behaves.
I also like it to shrink up and get crinkly and antique looking when the quilt is washed for the first time.
If I were doing a modern quilt that I wanted to stay smooth and flat, I would pre-wash the top fabrics, backing and batt to minimize the shrinkage.