I posted twice before you posted a second time. I was originally updating my first post, but then decided to just make a new post the conincidentally addressed your points from your second post. I guess I was anticipating what you might immediately respond with... and apparently I guess I was on the mark. Which would suggest iPlayer is STREAMING content, and not simply linking to an external FLV or MP4 file like most Flash content on the web. Moreover, I think if you have a sophisticated MEDIA SERVER that can apply certain rules and procedures in HOW media is served, you will have more content protection options that simply using Flash to link to an FLV or MP4 sitting in your normal IIS or Apache web directory. For instance, look at this tech note from Adobe outlining how users can work to "protect" Flash content.
http://kb2.adobe.com/cps/405/kb405456.html
Without these kind of measures (more involved than most people care to implement), you content is fairly naked. --Many websites simply choose NOT to focus on protecting content at the point of download however, and instead choose to rotate and expire dynamic links to the content itself.