I would say (b), that your team probably wasn't as good as you thought they were. Without intending offense, few individual developers or teams of developers are. :)

Some time ago I served in a Quality Assurance role, something for which I am not, by temperament, particularly well-suited. At the time, I supported five distinct development teams, each reporting to their own management structure. I found (without significant exception) that the teams who had prior experience with independent QA wrote substantially better code than the teams who had been permitted to roll their code directly to production without external QA. And I found that after one cycle with me looking over their shoulders, their code quality improved measurably. There is something about being held publicly and embarrassingly accountable that forces a developer to go back and check their work thoroughly. Developers will work harder to avoid even mild shame and ridicule than they will to save their own weekends from post-release bug fixing sessions.

If you're finding egregious errors, it is likely because of a lack of decent QA, or the lack of accountability for failing a QA pass. I know that the developers I supported playfully vied with me and with one another to make it through a QA cycle with the fewest number and severity of defects found. On my side, I thoroughly enjoyed the thrill of the hunt, ruthlessly seeking the soft underbelly of the code and mercilessly exploiting its weaknesses, as any self-respecting QA person will.

As an aside, if you're looking for good QA, look for a person who has that distinctive evil propensity for smelling blood in the water, the person who delights in destruction. I used to work with an excellent QA guy who had that peculiar bent; whenever I want to test software, I think, "What would Kevin do?" Usually, the most diabolical test occurs to me in short order once I get into that mindset. Most developers are so caught up in building that they cannot really conceive of actively working to break their own software -- it really does take a different way of thinking to test software thoroughly.