That's funny. As far as I can tell all the tools that are used for HTML (text editors and IDE's mainly) seem to be working pretty well for HTML5. And if you mean WYSIWYG then that market is dominated by Dreamweaver and even that has added HTML5 support.
Because you CAN churn out HTML5 in different text editors (or Dreamweaver) doesn't mean they're a GOOD way to generate rich content.
While I think Flash (the authoring tool) is a bloated mess, it's light years ahead of anything that exists for creating interactive content with HTML5/CSS/Javascript. There are no good tools for generating something like the Wired app in HTML5.
Actually, the Flash Builder app in CS5 can output to Canvas, but unfortunately, the latest version of mobile webkit that renders UIWebViews still has fairly poor Canvas rendering capabilities and performance.
Odd. I don't remember seeing that. My apologies :-)
I don't agree the tools are non-existent, but to the "wwhat do you gain from that" part: distributing a packaged "Web site in an app" has significant App Store and UI benefits over a paywalled Web site.