P.S: Again the future of IE comes into play. Will they support NativeClient or stick to ActiveX stuff.
That still leaves games being developed natively for multiple mobile platforms that are bigger markets, more rewarding, and increasingly more important than Flash for casual gaming.
The fight really isn't whether you develop:
Flash + iPhone + Android + WinMo + whatever
vs.
HTML5 + iPhone + Android + WinMo + whatever.
That nullifies the only benefit of HTML5 - not having to do different versions for each platform.
Like it or not, casual games are becoming a much, much bigger market than "hardcore" games.
Bejeweled is one of the most profitable game franchises right now. If I were writing that game from scratch today, I would do it in Flash or HTML5. That gets you every desktop that matters, and the number of mobile devices that support those technologies is still growing.
My argument wasn't that casual games have any problem, but that Flash itself is just one component of an industry that is increasingly focused on mobile.