I somewhat disagree, it depends on how QA fits into your organization and how you scope its role. UX needs Quality Assurance too, and sometimes things get past the UX team and into a product - at that point new issues come to light during testing and should be fed back up to the responsible teams.

In general I view QA as the last line of defense before the customer, if your QA doesn't speak up about ANY issues with the product, technical, UX or otherwise then who will?

Of course, my view of the role of QA in product design may be different from others.