Except... they don't write the grading guidelines. Where are these guidelines that you're referring to? The only ones I've ever seen on the CGC site are broad definitions of each grade. The only detailed grading guidelines I can think of offhand are the Overstreet standards, and CGC doesn't use those.
If I'm mistaken and CGC has published a detailed set of rules for the way they grade, I'd love to see them, so by all means share. If they did, though, I can't imagine that they would note 3.0 as a maximum for Marvel chipping, because I've seen many slabbed 5.0's with Marvel shipping comparable to that Hulk issue. Hell, I could dig up a few images of 5.0's of that exact Hulk issue with more or less the same amount of Marvel chipping. Even a 5.5 or two with a bit less.
(Now if only I hadn't fussed so much over the Marvel chipping that I completely missed the reading crease...)