But I also think that even if they don't, it also seems very possible that vulnerabilities are quite common as mistakes. Just due to the realities of security.
In my opinion security is much more difficult than people realize.
For example in this case there seems to be a majority opinion something along the lines of "What an idiot! _I_ would never make that mistake!". It's much easier to say that in hindsight than it is to really execute secure code that no one can defeat. The response might be "well, no one broke into any of _my_ systems so far" and I would say .. how do you know they didn't? And also, maybe no one bothered to try to exploit you because you are not a high value target. Or they are just busy and will get to trying to penetrate you next week.
I think this is due to the complexity of software and IT rather than general negligence.