Still, it happens - often because "they need to get a "C" to graduate" (or some variation involving a scholarship, Dean's list, or so on).
Rate Your Students has a pretty good piece on this topic that nails it. You can read the whole thing here, but the money quote comes at the:
Priceless. I think I'll use it.
Up until now, I was always suckered into actually engaging in the debate. But this fall I'm going to try a new tactic, and anyone out there who wants to is free to adopt it, 'cause I think it's going to work, and save me a lot of frown lines and email editing. Rather than getting into the specifics of their grades, I'll write the following: "It looks like you're asking to be graded under different guidelines from those in the syllabus, which were used to calculate the grades of the other 170 people in your class. Is this correct?"