And QA would be able to detect these worst kind of bugs? I'm not suggesting that QA is useless, I think QA should guide developers in terms of testing, as in Q

And QA would be able to detect these worst kind of bugs? I'm not suggesting that QA is useless, I think QA should guide developers in terms of testing, as in QA should help writing the test-cases including the corner-cases in spec and let the developers write more tests around those things. I also think that QA should help performing benchmark tests, load tests, and probably write end-to-end automation-tests (what do they call it these days? Acceptance tests?) Last but not least, QA should redefine the software processes if bugs happened regularly in a particular area. Consider QA to be a manager that responsible for the productivity of your software team: if a software process doesn't work (let's say one day you found out that TDD doesn't work well), QA should detect that and figure out a better way. Unfortunately, QA these days are still old school button clicker and test-case fanatics (i.e.: prepare 1000 test cases and ask the director for a week to run them all). But at the end of the day, bugs exist. No amount of human or practices would cover those exotic bugs.