"Average" is often considered to have the same absolute value as "bad". Most consumers will skip "average". This means that there is often a perception adjustment where publications don't want to place a game into the expanded "bad" range. That leads to a certain amount of inflation.
The whole structure, besides being entirely relative, is about as trustworthy as a feral ghoul. Because of other factors like publisher influence and terrible behavior from fans, I have very little overall faith in the honesty of the numbers we're handed.
As always, the words in a review are far more meaningful and important.