I agree with the anology that like the relationship between PgM and PM, QA is more stategic and QC is more tactical.
I work in Quality Assurance, and my experience has been that most Quality Assurance teams are actual Quality Control.
In fact, I've found that Quality Assurance is an attribute that is refined as an organization's software development methodology matures. It is a much simpler task to evaluate variance in a product from a defined requirement (QC) than it is to prevent the variance in the first place (QA).
As a leader of a Quality Assurance team that is responsible for both QA and QC, I see that both perspectives are required. Most importantly, just as a Quality Control analyst needs to also keep an eye on the strategic, so should a good Project Manager. In large corporations, some roles are specialized (PgM, PM, QA, QC) where individual people (or even teams) could take responsibility for each of these attributes.
On my team I try to focus our efforts (Quality Assurance) as a matter of emphasis than of turf. Quality Assurance is something that can only be successful if the entire team is evaluating how they can help to build a better product--just as a company can only succeed if all of the contributors are attentive to it's strategic goals. Saving Changes...
P Farrell-Vinay is correct IMO as a practitioner of QA for the last 10 tears.
This is also the definition supported by industry models like SEI CMMI-DEV, industry methods like OGC PRINCE2, and industry standards like IEC ISO9001.
Other definitions are still floating around, mostly because of the historical interchangeable use of QA and QC in the manufacturing industry. For example, if you look at a few plastic toys you'll see "QA Inspected" and "QC Inspected" labels; this shows a universal lack of understanding, and ignorance as to the benefit of having a different purpose and scope for each one. Saving Changes...