If Opera signed a deal with Steam and bundled it in their browser, would all the Steam games now "run in the browser"? Technically in some boring sense perhaps, but it wouldn't be on the web.
Do you know which Chrome-specific feature they are using? I'm not sure, but I expect it's user-convenience features like out-of-spec persistent storage extensions and notifications.
My point is that Skids is a quite high-end 3D game written in JS&WebGL that is playable today. It's a big step up from the dozens of "spinning teapot"-style demos most people have seen come out of WebGL so far. Technically, in some boring sense, it's not "on the web". But, it's great progress and a showcase of what can be done very soon, if not today, in Chrome, FF, Opera and Safari if people start trying. Maybe it'll never be possible in IE or Lynx. But, I'll take what I can get.
> Do you know which Chrome-specific feature they are using?
No idea. But they literally list Chrome as the only supported browser, so this looks pretty Chrome-specific.
There are lots of other impressive 3D JS&WebGL apps out there that are not specific to one browser, most however are tech demos and not fully finished products - I expect that to change before the end of the year though.