It's interesting that I can see academic grades reflecting the choice for 7/10 to be "average". When most people go to school they're given the message at some point that F is fail, D is mostly fail, C is average, B is above average, and A is excellent. Some parents/schools/other external sources try to push this scale up as the joke goes about Asian parent's grading system: F is for F***** because that's what you are when you get home, D is for Dead because that's what you might as well be once your parents see the grade, C is for Cr** because that's the score you got, B is for Barely Acceptable so you better try harder next time, and A is for Average.

But going back to the traditional, C is average, I think that going through at least 12 years of school where this kind of system is in place does have an effect on how reviewers choose their "average" rating. Usually when asked to choose something on a scale from 1-10, 1 is the lowest possible value, 5 is average, and 10 is the highest possible value. So theoretically, game ratings should follow the objective full scale and use 5 as average. However, I think this isn't used in practice because of school's influence to make you think that 7/10 is average and anything below that goes toward fail (below 6/10 means fail). So I wonder if the rising expectation for students to get 85%+ on everything is also having an effect on readers expecting that above average games should get above an 8 because they're taught that an 8/10 is not good enough.