Kind of reminds me about 20 years ago, when we went 'Oh my god, it's a spinning cube! In 3D!'
Why not build a castle from bamboo sticks? Building it from stone is better, but nobody has done it with bamboo sticks!
I think you're missing the point. 3D games in Javascript isn't about the delivery of the best technical performance (no script language will ever provide that), but about delivery of 3D multimedia content that is truly cross platform and accessible anywhere. It doesn't matter if you have a Linux box, Windows, Mac, Amiga, your mobile phone or whatever - if the system supports Javascript, you can play the game. Because it's online, you can play your game (and saved games) from anywhere and also compete with other people via AJAX.
Also, this isn't about providing gaming opportunities to the hardcore gamer, but more about opening new opportunities to general people.
Then again, maybe I just think of it different because I work as a full time web developer and not a desktop applications developer :-).