Yes, some fabrics do not play well with others. When getting the reds I'm using in my current project they where running red even after 4 washes, but seeing as the quilt will be red and white I had to get the red to stop, or else the entire quilt would have been ruined in just one wash.
I like the prunded, wrinkled, smooshed look of a quilt that wasn't prewashed, but so far I haven't been willing to ruin the quilt to make one.
Also while I work I do regular checks to make sure my quilt is "growing" to be the size I want it to. It would be very upsetting to me to think I had grown it big enough only to wash it and discover it was now to small, put post quilting and binding there's not much I'd be able to do about it. :(