... We, as developers, will have to waste our time supporting these browser differences...
I'm puzzled by this as well. From the perspective of someone who creates video, the HTML5 case is:
"Encode your video in multiple formats to support all browsers"
versus the current case
"Encode your video for flash"
Without a plugin model for adding new video decoders, I can't see how HTML5 is a Flash killer. Flash is EASY. Am I missing something here?