As of May 2010, 26% of all web video is now available for playback in HTML5 using the H.264 format up from 10% on January 2010. This is a meteoric rise to adoption for a technology. Out of the sites that support HTML5, iPad users are detected and switched to an HTML5-compatible format. YouTube has even enabled that functionality on their embeds from other sites.
Apple iPad has forced rapid adoption of HTML5 video.
For most news type sites, only recent stories are available as most back library content has not been encoded to be used in HTML5. Another area lacking is that there is little HTML5 supported episodic content available from major TV networks. ABC has an app, but no full episodes are available from their website.
Source: Mefeedia Blog