No one who has been paying attention expects CGC ( or practically anyone else) to guarantee they will grade a book the same way twice. Grading is too subjective, and prone to shifting assessments of what the sum of the flaws should mean. In part the faith in CGC's grading is that it is impartial, not that it is absolute. It would be nice if CGC appeared to be a bit more consistent some times, but that's what you are going to get with multiple graders, even if they are using the same criteria. To repeat, there are no absolute grades, the best we can do is find a fairly tight ( generally 2-3 grades) range that most knowledgeable people can agree on. Does CGC sometimes fall outside of a general consensus of what that might be? Yes, and a 7.0 for this particular book may be such a case, but it is hardly unique, and even the most trusted and consistent of graders may at times find their opinion at odds with the bulk of the collecting community.
And that is why we buy the book and not the label.
The big issue is the difference that the market creates between a 6.0 and a 7.0. My LCS and I had a discussion recently about how people seem to see 7.0+ as more collectible while the price gab between a 5.0 and 6.0 isn't all that extreme.
Of course we had no evidence to support it. It was just a discussion but there does seem some truth in it.
A 7.0 is in the "VF range", while a 5.0 and a 6.0 are in the "FN range". I am always amazed at what a good deal the minus (-) grades can be, because of the "stigma" of the minus. You can often buy a 9.2 cheaper than a 9.0 (on any given day).