It looks like depthAndStencil option is only available with AIR 3.2 onwards.
Looking through the template file that is used to generate the app descriptor file:
[AIR SDK ROOT]\templates\air\descriptor-template.xml
The entry for depthAndStencil first appears in the template file that comes with the AIR 3.2 SDK.
Edit:
Confirmed. See release notes for 3.2 SDK: http://helpx.adobe.com/flash-player/release-note/release-notes-developer-flash-player.html