Yep. I did a render of some mechs a while back using no lights. But it comes out fairly grainy.. It's better just to use a couple lights. And as with the bear pic. That's not really lit by ambiance as much as it is just reflecting other brighter objects. You can however fake it by turning blurry reflections on and making the specular halo of the bear materials completely white. This changes the angle of reflection to (approaching) 180 degrees. Whereas without it it reflects a direct line based on the angle of the camera. This is the best way to "fake" radiosity, however unless you render it at 256 rpp, it will appear extremely grainy. (which some people like)