I know roughly five [QA testers] who moved into other roles, usually low-level designers and one as a concept artist.
I know one who became a producer on AAA titles.
I know one who became president of a studio.
I know one who became a VP of a AAA publisher.
I know one who became a producer at a studio.
QA isn't for everyone. It isn't a guarantee of advancement. But for many, it's a foot in and a leg up.