Thanks for the feedback. Perhaps. It's one of the three possibilities:
1. Stabilization is always on.
2. Stabilization is only on for "apple native" apps (native camera app & FaceTime)
3. Stabilization is off. The field of view of iPhone 4S back camera (in Skype, Google Hangouts & FaceTime) is the same as the camera mode of iPhone native camera app. My understanding is, when digital stabilization is on, the field of view narrows, like in the video mode of the iPhone native app.
I hope this helps?