Turning off the http referrer check won't guarantee that forms submitted came from your site(s) only.
"Spam" is the "danger", it is not recommeded to ever disable the httpd referrer check.
And yes, you should try it with both the www and non-www in there, i have multiple as:
http://www.undergroundnews.com|http://www.undergroundnews.net|http://www.undergroundnews.org
I don't allow users to access my site without a "www" on the domain, you could update it as:
http://www.undergroundnews.com|http://undergroundnews.com