I was always disappointed with Apple Keynote pages. It allows you to stream and watch the videos with QuickTime which is not great for streaming and videos are not HTML5 yet. Another restriction with QuickTime is, you need to have QuickTime Pro to save the video.
Yesterday I found how to download their Keynote videos with iTunes. In fact Apple podcast all their keynotes (many of them) with an iTunes Channel and videos can be downloaded for Free*
But there is one issue, I was not able to find the low/Medium only Hi-Def available WWDC 2010, Jun 7 – 1.27Gb