See this page: https://developers.google.com/structured-data/schema-org
Google is in the process of adding JSON-LD support to more markup-powered features. So far, JSON-LD is supported for all Knowledge Graph features, sitelink search boxes, Event Rich Snippets, and Recipe Rich Snippets; Google recommends the use of JSON-LD for those features. For the remaining Rich Snippets types and breadcrumbs, Google recommends the use of microdata or RDFa.
From this, I understand that I should only use JSON-LD for events and recipes.
However, looking at examples that Google themselves provide for other types (https://developers.google.com/structured-data/rich-snippets/articles#article_markup_properties) it seems they provide JSOn_LD examples.
Also, using their testing tool (https://developers.google.com/structured-data/testing-tool/) seems to work fine.
So, which is it? Did they forget to update the intro page? Or are they giving bad examples?