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="271" ns="6" title="File:MMW Logo Stacked.png" />
      <page pageid="3" ns="6" title="File:Medium MMWlogomedium150dpi.png" />
      <page pageid="244" ns="6" title="File:Selection 001.png" />
      <page pageid="245" ns="6" title="File:Selection 002.png" />
      <page pageid="246" ns="6" title="File:Selection 003.png" />
      <page pageid="247" ns="6" title="File:Selection 004.png" />
      <page pageid="248" ns="6" title="File:Selection 005.png" />
    </pages>
  </query>
</api>