An XML language can be created to express Bookstores. 

.....which allied with an XML schema can semantically represent books, magazines and newspapers as types of Publication (remember). A JSON document with or without an accompanying JSON Schema cannot do that.

Of course it can, it just does it differently. Instead of capturing the type of publication using the element name, you capture it with an extra attribute/property named "publicationType". You can argue about which representation is "better" (for example, better at conveying the semantics to the human reader), but they both capture the same information -- and neither conveys any semantics to the human reader unless they know what the element and attribute names are supposed to mean.