This should have "Atom-Powered Robots Run Amok" under it from both application/atom+xml and text/xml:
Internet Explorer (6 and 7) only load the document served as text/xml! jQuery is used to make this demo simpler, but jQuery is just using "new ActiveXObject("Microsoft.XMLHTTP")" and responseXML like anything else. The jQuery docs note this, suggesting you manually parse the document with Microsoft.XMLDOM.