Not really sure what caused the big concern is either. Various reasons,
1.) some folks only want to use "natural" fibers,
2.) some are concerned about the different fibers will wear
3.) others that do not pre-shrink their fabric are concerned they will shrink unevenly.
I am sure there are other reasons.
Sometimes I can only find a certain shade of a solid fabric in a cotton blend, so that is what I use. So far none of the folks I have given a quilt to has had a problem.