[DickHaynes]

I agree with Wedding Shooter. Also, IS does NOT only counteract the movement of the camera. So it does matter what size lens you are using. When you are using a super telephoto lens camera shake is less of a factor than that of the movement of your lens. If you were using an extremely small focal length you can use a slower shuter speed, why? Because you are using a shorter focal length.

End statement: If you are using a huge lens, you need to be able to have a huge IS element to compinsate for the huge amount of movement.