HTML5 supports natively and easily embedding and playback of certain popular video formats now without the need for any plugins like Flash.
It is supported by all modern browsers and although they don't all support a single common video format there are only 3.

This would be good because directly embedding video into a SWF container is not only somewhat difficult to do properly but additionally only offers very low quality.
Also, youtube probably wouldn't like a lot of content of a certain nature being uploaded to their site just so we can display it here.

So allowing us to host our video content on servers where we can simply provide a .mp4, .webm, and .ogg link to weasyl for a submission would be wonderful!