How can it possibly make sense to zip the video files? It ruins any chance one has of progressively downloading as you watch, and it can't save any bandwidth.
Your second point is valid, I hadn't considered it as a serious problem. I think a better solution than a zip file is to provide a "download" link pointing to the file that serves it with the Content-Disposition HTTP header set. This requires some control over the web server (e.g. ability to run script, or set up an htaccess file), so it's not always an option.
Edit: sorry for complaining on HN rather than contacting you directly. I was venting because it's frustrating that I couldn't watch the first few minutes of the video to decide if it's worth watching/downloading the entire video.