HTML5 Video has not been able to show its potential because of the large numbers still using IE8. Yes there are solutions to show a video by embeding it in Flash for IE8; But, HTML5 video can go beyond just showing a video.
Exposing controls to a video to script on the page allows the video to be interactive with other content on the page or interactive outside the video box. Site menus for example can turn on or switch video content based on where the user is focused via looking at scroll bars or where the mouse is on the page.
One a related note Netflix drops silverlight and moves to HTML5
The major objection to HTML5 video is protecting or preventing the video from becoming copied. However that is being solved.