Wasn't the basic idea of JSON to be small and unstructured to be sent between applications? Shoehorning everything into JSON that is already solved by XML seems illogical, as GP already said. It reeks of NIH.
People shouldn't use JSON for anything hand-written. YAML or even the older INI format are way better suited for configuration files for one reason alone: they allow comments.
To me, JSON can be viewed as slightly enhanced S-expressions, enhanced in a particular way. It would sound strange hearing "shoehorning everything into S-expressions in Lisp that is already solved by structural Fortran syntax seems illogical".
NIH claim is probably valid when there are no noticeable difference. In my opinion, XML differs a lot from JSON, particularly when one need to write snippets by hand. JSON also seems more logical/laconic (once upon a time M-expressions were supposed to come to stage, but S-expressions turned up to be good enough).
People shouldn't use JSON for anything hand-written. YAML or even the older INI format are way better suited for configuration files for one reason alone: they allow comments.