That's the thing. You don't escape from those problems in native environments. You still have to deal with different GFX drivers doing different crap on different platforms, cards that they that support a GL extension but don't, etc. And that's just OpenGL.

With the browser, you're just adding another abstraction layer that has even more complexity. WebGL is far for a decent spec. And we're talking just graphics, as I mentioned before, audio and networking have tons of unstable and untested code.

Multimedia programming is already hard on native environments. I don't see the web being a friendly environment anytime soon. There's no silver bullet, "code once, run anywhere" for games and multimedia.