I hope others more knowledgable will reply, but upon reading, I would offer the following possibilities:

• the server may be using named-based virtual hosting, which would (I believe) require a HTTP/1.1 header with a "Host: sitename" key-value pair prior to the request, and
• the page/site may be using cookies for maintaining state and requesting that information further on

I would recommend chapter 20, "Web Automation," in Perl Cookbook, or Web Client Programming with Perl (the latter I understand is no longer in print, although there may be some information regarding on the O'Reilly website). Some of the links here, especially in the Outside Links section, may also be of assistance.

I hope this helps somewhat, and good luck.