It doesn't change the context that the instructor isn't being paid to do it - he says he's already spent more time on the course than contracted. From his point of view, it's not an unreasonable request that he should not spent more of his (insufficiently remunerated) time on even small issues.
> and would be understandably pissed off if I was given no opportunity to collect an exam I'd taken.
But does that make it reasonable to blame a guy who's not paid to help you for not helping you?
I do understand the nature of your point, but I don't think any of the original argument is actually affected by the size of the task he's refusing to do.