Does camera mechanical IS allow to reduce ISO by 2 stops eg. from 800 to 200 ?

Question

If that is so, then the IS camera will use 200 ISO when non IS camera will use 800 ISO. The IS camera will produce less noise. So in theory, 10 Mpx IS camera with average noise performance , in the same light conditions, will produce better picture then industry leading low noise 6Mpx non IS camera?

Answer 1

You're correct. With image stabilization turned on, you can use slower shutter times with handheld shots. In turn, this lets you use lower ISO settings and/or smaller apertures. Two stops sounds about right.
Of course, image stabilization will only mitigate camera shake. It doesn't do anything for subject movement. So if you're shooting people, image stabilization can be completely counter productive. It's better to have a grainy shot of everything (using ISO 800 @ 1/60th) than a crisp shot of the background with blurry people (using image stabilization, ISO 200, and 1/15th).
If you do a lot of hand held, low light photography, perhaps get a camera that's better at high ISO. A Fuji F30/ F20 or a dSLR, for example.
The real purpose of IS on a mega-zoom point & shoot is that you NEED it with those long tele zoom lenses. Try shooting a 400mm lens without IS or a tripod.