The Correct Answer or the Most Helpful One?

I almost always do what you call the "correct" option, rarely the "helpful" option.

I think it's kind of like the scenario where someone asks you, "Can I see that?" I answer yes, but never hand it to them, since he or she never asked to handle it. And if I'm taking this in the right direction, it's kind of like when you ask someone something, and they don't give you the direct answer, and instead say something else that's slightly relevant, but not the answer you want, like the bus/train scenario in your opening post. I hate it when that happens. It really pisses me off, so it's built me into the kind of person that gives the direct answer instead of the "helpful" answer.