The IE10 available with the developer preview of Windows 8 doesn't support webgl. If there are no plugins, and Microsoft don't want to enable webgl support (like they have claimed), the Metro environment would be crippled. Although webgl is mostly used for demos at the moment, and doesn't have usable support on iOS and Android, there will come a time when webgl support is expected. I'm sure Metro alternatives with webgl support will show up, but it will probably be a long while before we know the possible state of webgl in IE10.