I've had some kernel panics from WebGL content too (acko's mathbox2, as well as normal OpenGL apps) on Linux w/ nouveau open source drivers. I changed to proprietary drivers which seem to work better. Having the latest version of browser/os is no guarantee that it works.
Not, it's not why they objected, since they had already exposed the same features in Silverlight.
The ability to hang your machine only requires the ability to ask the GPU to do lots of work. No shaders required. Even given an API that only allowed you to submit meshes you'd just build a mesh of layered polygons and zoom in to fill the screen. There's no way to limit such an API and still have it be useful.
Fortunately as pointed out then and above there's no incentive to crash your machine. Baddies get no info, no access, all they get is no one coming back to their site.
