Fable III has Vert- cutscenes and stretched FMVs in surround, however actual gameplay is Hor+ with an unstretched HUD. In fact, HUD that didn't show up in widescreen showed up in surround, as can be seen in the comparison screenshot. Not sure what it means yet.
Included with the game is a "Video Options Applet" which can be found in "X:\Program Files (x86)\Microsoft Games\Fable III\PCVideoOptionsApplet", and allows you to select your desired resolution, including surround resolutions. However, in-game you cannot choose surround solutions, surround resolutions will just show up at 1366x768, and changing any video settings resets you to 1366x768 (it did for me, anyway).
Alternatively, surround resolutions and detail settings can be edited via an *.xml edit. Find the file "VideoOptions.xml" in C:\Users\YourUserName\AppData\Roaming\Lionhead Studios\Fable 3, if for some reason you should desire to do so.
Find the following values and input your desired resolution:
Code:
XXXX
XXXX