I'm having issues viewing the videos here too. What it does is plays the first few seconds of video 1 and then the first few seconds of the next and so on... and keeps looping through them i the pop-up window.
http://www.omnigroup.com/products/omnigraffle/videos/
10.7.2
Right-click an view in QuickTime works. But I'm guessing it's not an issue with the current QuickTime, but the way the original videos were encoded and/or embedded in Safari 5.1. I see that the date in the video is May 2008 in Don's videos.