The issues to date have been selling PGX books(not allowed), selling PGX books but not showing the label(not allowed), and recently posted books shown in PGX holder (one seller indicated book was unslabbed but no new pic was posted, other indicated book would sell as-is(slabbed) or raw(cracked) based on buyer's preference).
If CGC truly feels that any of the above scenarios are unacceptable, then maybe stipulating "raw or CGC only" requires photo of item in it's current state to clarify any potential questions. Flip side is to drop the "raw or CGC only" guideline, depending on how strongly CGC feels about PGX books listed here. (We know how Steve feels. )
On the other hand Sal's post brings up a good question? What constitutes "raw"? I have never tried to crack a slab just enough to remove a label and leave a book in for protection, but is that unreasonable?