All the HTML5/WebGL stuff may be nice for casual gamers, but as a gamer I really don't want all that stuff. Same visual quality/performance as a native game is probably not possible and every game in js will perform worse AND create more load (and waste energy). Why is everyone trying to move games and big applications to the web?
However I can see exactly why people are doing this. There have been a big explosion of indie games recently and that can be put down to iOS and Steam. Both make it super easy to get games.
Anything that reduces friction is going to be very appealing to game makers. And installing Steam is friction. If playing your game simply involves visiting a link - thats pretty easy. As HTML5 matures, as more people use modern browsers, and as Flash becomes less reliably installed on browsers, expect to see a lot of casual games moving to HTML5.