This seems to be tacked on to Flash so I'm curious as to how it compares to Hype (http://tumultco.com/hype/), which is an editor designed exclusively for HTML5.
I've also been making an HTML5 animation design app called Radi [1]. Compared to CSS3-based animation tools like Hype or Edge, Radi is more similar to the Flash Pro environment because it has vector drawing tools and supports more forms of animation (e.g. shape keyframes). Radi also does video.
Just a word of warning: Don't expect much in the way of future upgrades or improvements to this. Adobe have already stated that they see the future of Flash as being a games and high end video solution. They expect HTML5 specific tools(Read:Edge) to solve everything else. I just went to Adobe Refresh where they re-iterated this in very unambiguous terms.
I think he may be trying to get at the fact that we have 5 major browsers (IE, Chrome, Safari, Firefox, and Opera) and 5 platforms (Windows, Mac, Linux, iOS, and Android) that "web designers" build for.
Compare that to one virtual machine (Flash) if you wanted, which although not "standardized", is controlled by a single company. iOS developers make this argument all the time as to why iOS is better to develop for.
Flex is a different beast (to my knowledge). Adobe would have to somehow support the huge library that Flex already has. A reason why not all components of AS2/AS3 are not supported.
Flash CS5 uses the new XFL file format, which are essentially zip files. The DOM document is then just parsed through and converted into their counter parts.
