Interesting to see that YouTube has made their embed code default to an iFrame instead of using an <object> tag to insert a Flash player. This capability was introduced this summer, but it was more experimental then and only became the default experience last week.
The main motivation for the switch?  So that if you are on an HTML5 browser, you won't be sent Flash, but rather your browser will use the <video> tag and serve up either WebM or H.264.  Read more here.
What's interesting is that HTML5 on YouTube's site was an experiment, but with making their embed code an IFrame by default, it means HTML5 video becomes much more prevalent.The average Joe user who wants to embed a video on his blog will now be serving up HTML5 whether he realizes it or not.