I don't have Flash or Silverlight installed on my system. Trust me when I say that approximately zero commercial video is available with these plugins.

Even half of the ad-supported content on YouTube isn't available.

As an implementor, until mozilla finished shipping native h.264 support I have to either use Flash as a fallback for IE8 and Firefox (mediaobject.js is great!) or encode all of my video twice and double my storage bill. Guess which one is more appealing?