[slibhb]

I don't see any evidence that Tyler is surprised by this. If you read his blog, it's wide ranging and the fact that he's linking something doesn't imply surprise. To me, the surprising thing here isn't the humanities. It's Math (52%) and Physics (67%).

That aside, I don't think your explanation is good. There are many forces behind grade inflation. Some of them are safetyism, suspicion of inequality, cheating via the internet, widespread subjectivism (who's to say who's right or wrong?), and so on. Probably the biggest factor is affirmative action. Having accepted a large number of students for reasons other than their academic performance, it's not possible to simply give them worse grades. It would look bad. The result is high grades for everyone and the creation of pseudeo-academic disciplines where everyone gets an A.