JSON’s untyped nature flows with how the web itself works. The web does not seem like typing; it doesn’t like schemas; it doesn’t like things to be rigid or too structured. Just look at the failure of XHTML. A beautiful idea for the purists, but for the web, its lack of adoption underscores its platonic ideals.
I’m odd I guess since I still enjoy working with XML. Considering our API integrations at StatsMix though, JSON is definitely the prevailing format.