Security engineers are seen as experts you consult about something you don't know. QA are not seen this way. Some QA engineers actually are experts that can give good advice on structuring an application in a more testable way, but that's not the norm.
Most QA guys only check that something meets the spec/story requirements, not that the code is sane or testable... many don't even go beyond UI testing. That said, I think GP was referring to having a QA embedded as part of a team.
