[roundsquare]

"Why isn't blaming professors for cheaters analogous to blaming rape victims for being insufficiently vigilant against rape?"

I don't think the analogy holds well. The point is that a professor is supposed to help his/her students when they have questions. If they don't do this, they increase the probability of cheating occurring. It's less of "blaming" and more "noting" that this happens. If the professor is partially ignoring this duty, he/she is partly to blame. (I'm not saying that happened here, just explaining what I think @reason's logic is).