That's for Flash video (FLV) which ironically is not a streaming video format. (You can get at the whole file all at once.) WMV9 can have streaming as a property of the video itself, meaning that when you download the video, you get something like a 1 KB file, to get the ball rolling. Getting the streaming video data must be more than a passive download process (?).
This page claims to have the answers. Check it out.
Edit: The link to GAS there is dead. After some frustration with Japanese sites, I found
this link to an even newer version. The UI is in English, although release notes and help are not.