It's fine to say "Look this is bad, don't do" and "A patch was issued for this, you are responsible" but when some set of circumstances arises that has not been thought about before that cause a problem, then there's nothing that could have been done to stop it.
Note that the entire QA industry is explicitly geared to try and look at software being produced in a way that nobody else has thought to, in order to find if that software still behaves "correctly", and <some colour of hat> hackers are an extension of that - people looking at software in a way that developers and QA did not think of.. etc