In response to previous questions regarding FMS security, the reasoning behind the restrictions on interacting with RTMP streams is to protect the content being provided by the server. This is a little different from other data loading operations as RTMP is not directly covered by cross-domain policy files and was not originally intended as an interactive data source (rather than just a hands-off media type).
In theory permitting access to the RTMP stream does not pose security issues so long as the Flash Media Server can reliably specify a preference for who is permitted to interact with the RTMP streams. So don’t be surprised if this restriction is relaxed in the future.
For detailed information regarding protection content served from Flash Media Servers, see http://www.adobe.com/devnet/flashmediaserver/articles/protecting_video_fms.pdf