Well no, none of the reviewers have come out and said "we only grade on a scale between 7-10 when it comes to major triple A releases" but its commonly known that they do, i dont expect reviewers to be self aware of any of this. And 6's and 7's are bad, these are bad scores for video games, there is no two ways about it.
Ive read the reviews, and it sounds like a much lesser game than the previous 2. It does nothing new and even the stuff it does is of lesser quality than previous games.
Even FIFA and CoD, which are very similar to last years releases get 8s and 9s, and have for years.