I see a large number of problems with the belief that HTML5 will defeat Flash. It will become another competing format, just like Silverlight, but I highly doubt it will defeat Flash in any real meaningful way (and even if it did, it wont remove the things people find a problem with Flash, other than possibly the searchability issue).
Firstly, most web developers these days will write javascript for a framework such as Prototype, MooTools or JQuery because there are so many individual nuances to the javascript notation for each browser that it would be too frustrating to write it without such a framework. This problem will still apply to HTML5 so unless these supposed IDEs pick 1 framework and run with it, we're going to end up with a complete mess of features, frameworks and IDEs. By the time one of them becomes as usable as Visual Studio or Flash CS5, Silverlight and Flash would have both moved on in leaps and bounds attempting to stay well ahead of HTML5.
Secondly, by the time HTML5 is ready for real use (i.e. supported by the vast majority of browsers currently in use), W3C will likely be back around the table discussing HTML6 so who knows what Flash and Silverlight will be capable of by then and what uses we will have for them.
Thirdly, at the moment, HTML5 is far more complicated to write for than either Flash or Silverlight, in most cases it has a significantly larger file size, uses more resources for most of Flash and Silverlight's current usages and it is a lot harder to obscure code or source material, meaning sites like Hulu just wont use it.
There is a place for HTML5 (I'd be happy just for an implementation of canvas in IE so we don't have do all our chart generation through PHP) but it is not, and is never really likely to be (as HTML5 and not a future variant) the death of Flash and Silverlight.
Lastly, I'm sure most people here are happy to use Flashblock to stop any obnoxious Flash site but what will you do when canvas,SVG and CSS (no need for javascript) can reproduce all those annoying flashy adds with little to no way to block them all?