bearisgray-- The logic in your question is exactly what keeps me from buying precuts. The reason for washing precuts is the same for me as when I wash yardage: test the fabrics for colorfastness, get the germs out, let it shrink before subcutting.
That said, I've been given precuts for Christmas. As much as I like the look of them and the temptation to just "get started on the next quilt and wash it with Color Catchers later," I KNOW what washing does to those pristine looking pieces. I deal with it when I bring scraps into the house, even when I use the zippered mesh bag. The time it takes to wash, partially dry, iron, and still get ravels, more than doubles the work. And I simply don't have the guts to chance whether JUST ONE fabric will bleed in my finished project.
Hence, you'll find precuts in my sewing room, but they're still nice and pretty in their packages!