The videos on Netcast are set up to operate much like a television channel; only to be streamed, not downloaded. The link that you are clicking on is simply a reference file that initiates the sending of the video feed, not the actual video file itself.
The reason behind this policy is that videos have copyrights attached to them that we do not wish to violate. We are allowed to broadcast them, but we are not allowed to distribute the programming. Even the University Lecture Series, which sometimes offers free and open attendance to the public, does not allow us to re-distribute any of the speeches that we record.