I suspect we're at the begining of a move of such environments onto the web.
The HTML Canvas element gets you some of the way there by providing a bitmap display. People are already building basic demos and infrastructure for 3D applications running natively in the web browser. It's a long way from simple untextured wire-frame models to WoW, but the direction is clear. Google (and many others) have already put IM into the web browser.
I'm getting a bit lost as to what the state of the art is here, YUI, GWT and OpenLaszlo look like interesting sets of libraries for building applications, but as far as I know there isn't a standardised interface to the hardware. OpenLaszlo mentions microphones, but is that only for the Flash target?