I've had no problem with their fabrics either. Some times fabrics feel 'thinner' but that doesn't mean they are poor quality, it depends upon the thread count. Also, their threads have been highly recommended by quilting pals. With so many quilt and fabric shops disappearing and quilt shows being discontinued, like Quilter's Hertiage in PA, we all may be depending upon online purchasing.
One time I would suggest not prewashing is if you ordered a kit and the pieces were precut. May in Jersey