More than likely it's because your server has the "proper" MIME type set to
Text Formatted Code
application/rdf+xml rdf
while the other site does not, so it uses apache's
Text Formatted Code
DefaultType text/plain
rendering any mime types not listed in the mime.types config as plain text.
If you have control over the server, you could remove that MIME type and it would render as plain text. If not, maybe an htaccess could override the MIME types, not sure though. It's late and I'm too tired to research htaccess stuff right now.
HTH,
Chuck
Too many hands on my time.