Blogs are an important channel of information on the web. However, because feeds (RSS, Atom in various forms) represent cross site risks to feed readers built on the web, not to mention the potential for javascript to mess up the HTML based reader's DOM, many feed readers strip out embed, iframe and script elements.
There is only moderate consistency in when this is done. For example, Google Reader subscribers won't see the embedded graph below from d8taplex, but Bloglines readers will.
Video is one of the most important media types online, and web-based readers - through a white list mechanism - permit embedding and iframe inclusion in feeds if they source their content from certain blessed sites. However, again, this behaviour (the content of the white list) varies between online feed reader services.
One of the promises of HTML 5 is the ability for more and more application functionality to be delivered via standard browser interpretable mechanisms including javascript, SVG, the canvas element and so on. However, if online feed readers are cautious with this type of dynamic embedded content, then the blogging channel is going to be stunted when it comes to innovations in discourses that involve non-textual elements.
As Google Reader is the dominant player, they would, ideally, set up some mechanism to establish the validity and reliability of sources of such dynamic content, thus allowing all legitimate contributors the means to publish via feeds. Otherwise, dynamic data providers are forced to use Flash or similar runtime based inclusions and not the HTML 5 stack.