Imagine if these were real commands:

    $ docker download-install-and-run-my-customized-build-of-postgres

    $ docker start-up-a-wordpress-instance-from-some-online-build-template
    $ # edit some config files, add some plugins
    $ docker pack-that-wordpress-instance-into-a-container

    $ ansible all -a docker download-and-run-your-wordpress-instance-on-all-your-app-nodes

That's basically what docker does; the syntax is only slightly more mundane, and is actually less verbose than that.