I have this problem and I have a Samsung Ativ S. I'm 90% sure that it is a Software Issue. My Camera stopped working ever since my phone updated. The Samsung Ativ S camera works in my local stores display (Demo Phone), which is an outdated version of Windows 8 (Cant remember the details, but long story short, my phone was a newer firmware). This convinced me that the update "Fixed" some problems, but introduced some New problems that I hope Microsoft and/or Samsung are working on. A smart phone without a camera is not a smartphone.
P.S. I also got my phone fully replaced. Same problem. Same firmware (updated version compared to the Demo Phone). The only way I could be wrong about this is if the two phones I've had were both damaged units. Even so, thats just a little ridiculus.
Further Info:
OS Verion: 8.0.10211.204
Firmware revision number: 2212.12.11.5
Hardware revision number: 15.3.1.0
Radio hardware version: 0.0.0.0
Bootloader version: 12.11.15.14
Chip SOC version: 1.5.32