Regarding how CGC grades them, I have seen printer's creases on books that they have graded up to the 9.8 grade. Whether you agree with that or not, that's just my experience.
I would imagine that regardless if you think that it would affect the technical grade, certain people would treat it differently from an esthetic point of view.
Regarding why it may show up on certain books more than others, it has been posted in the past from people in the printing industry that cheaper paper were used for the least popular titles. That's why you seem to see a lot of printer's creases on books such as Weird War Tales 1 and Ghosts 1. They probably weren't the top priority books at the time.