In recent times, this phrase has become more of a sarcastic comment made by programmers than an actual excuse one would use in practice. In a real customer scenario, when a bug is found, no one is going to get back to them with "No you see we intended the system to crash when you pressed that key 5 times the way you did..just you know..don't do that next time". It is a sort of self-deprecating joke that comments on just how often certain (unintended) consequences of design decisions are left unfixed because it is too risky and not worth the effort required when potentially no one would ever stumble upon it. It also comments on those times when the code behaves in a way that no one understands and no one can explain. It is one of those things that make new programmers giggle and veteran ones cringe. But, it does also serve as a reminder that programming with careful planning and design will lead to a product with no "surprising features".
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