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="17" ns="0" title="IJoomla Installer Installation" />
      <page pageid="449" ns="0" title="Migrations, Upgrades and Compatibilities" />
      <page pageid="153" ns="0" title="Poll" />
      <page pageid="38" ns="0" title="Setting Up Cron Job" />
      <page pageid="33" ns="0" title="Traditional Installation" />
      <page pageid="43" ns="0" title="Update With Patch Files" />
    </pages>
  </query>
</api>