> They aren't a standardized DRM scheme; they are merely hooks for proprietary DRM schemes, essentially a way to allow proprietary DRM schemes to hook into the HTML5 media player rather than having to use the plugin interface and implement the media player in Flash or Silverlight. It's basically just a plugin API for plugins that provide only DRM, leaving the rest up to the browser.

Exactly: its a specification for a constrained plugin API focussed DRM, so that browsers don't have to either maintain a common general purpose plugin API (e.g., NPAPI) or, alternatively, have browser-specific APIs in order to meet content-owners demand for a DRM-supporting delivery channel.