THIS remains a key issue. It is not difficult at all to create something that will garner a 10 from CGC. Just cut out a sheet of steel, sand the edges and corners with 3000 grade grit until it can cut through anything like hot butter, and attach it to your book of choice.
(Superman comes to mind as a natural).
9.9s and 10s are naturally rare as it is difficult to find comic book paper that can be printed and stapled into a book without even the slightest tears/imperfections. Once anyone starts to mess with this process, things become suspect. (I mean, how hard would it be for Marvel to produce issues by hand, insuring the creation of 10s? They could even market them as Marvel, Hand Made (tm))
When the company doing the grading actually becomes involved, things get even worse.
By the way, anyone who puts out a Man of Steel 1 with a steel cover at least owes me a copy.