I am normally a pre-washer as well. However, when I do the sampler at my LQS, they give you small cuts for the monthly blocks. But the finishing pieces are all yardage. I tend to not wash those since I don't wash the small cuts in the balance of the quilt.
BUT, I really don't think shrinkage is that much of an issue today - the way it was decades ago. I think the biggest shrinkage factor is the batting vs the fabric. And unless you have lots of red or are dealing with lesser quality fabrics, I don't think you'd have an issue with not pre-washing.