You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <pages>
      <page pageid="9" ns="0" title="Green River" />
      <page pageid="11" ns="0" title="Patoka Lake" />
      <page pageid="19" ns="0" title="Dix River" />
      <page pageid="22" ns="0" title="Kentucky River" />
      <page pageid="25" ns="0" title="Cave Run Lake" />
      <page pageid="573" ns="0" title="Lake Superior" />
    </pages>
  </query>
</api>