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-continue>
    <revisions rvcontinue="1411" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Main Page">
        <revisions>
          <rev user="MediaWiki default" anon="" timestamp="2005-10-16T01:16:23Z" comment="" />
          <rev user="Andy" timestamp="2005-10-16T01:47:31Z" comment="front page content to here for now" />
          <rev user="Dana" timestamp="2005-10-21T01:30:01Z" comment="" />
          <rev user="Andy" timestamp="2005-12-15T01:02:43Z" comment="Xen hosting &amp; email policy" />
          <rev user="Andy" timestamp="2005-12-15T13:02:01Z" comment="/* Hosting info */ Other sources of info" />
        </revisions>
      </page>
    </pages>
  </query>
</api>