You make many good points. I think they are all valid, including the importance of test engineers and thorough testing. A programmer self-tests his code, but that isn’t enough.
I just want to add one comment about testing. In my experience, no matter how much in-house testing is done, customers will find some bugs. Always. There might not be any major problems (this isn’t about LingQ), but there will be some bugs. Why? Because customers always use the thing in ways that nobody at HQ thought of. Not engineers, spec-writers, tech writers, QA engineers…nobody.