Managing web content is about more than simply supporting the technical constructs the web uses (REST, stateless etc.).
eg. the graph of relationships between the content items making up a site can be an important source of information for authors.
But the web itself has no direct support for graph data structures (beyond humble 'pointers': <a href> tags and the like).
And perhaps as a consequence many (most?) Web CMSes don't have support for that either. 😉
IMNSHO the future is: schemaless (ala CouchDB, MongoDB, at al), graph based (ala Neo4J), distributed version control (ala Git).