Google's feed reader lets you view videos from YouTube and Google Video, if they are embedded in a post. Until now, the feed should have contained enclosures, which is not possible in many blog softwares, including Blogger.
Feed readers ignore some code (embedded objects, JavaScript, iframes) for security reasons. Google Reader made an exception for YouTube and Google Video, but they should consider other online video sites and even other kinds of content.
{ Thank you, Huw Leslie and Rick Silva. }
Update: Google says you can view embedded videos from other sites like MySpace, Metacafe, Revver and more.