I am getting a Truvativ Styli 1.1 gxp SS crank for a build and noticed it recommend me to use a 3/32" 9-speed chain. I would have thought you would use a single speed chain on a single speed crank. Looking around at other cranks I have found that many of them also require or recommend narrow chains. For example:

Crank: Chain recommendations
Sram S300: 9 or 10 speed (even though "track" is stamped on the ring)
Sram S100: 3/32" chains
Truvativ Styli oct: 9-speed 3/32
Truvativ Descent: 9 or 10 speed 3/32
Truvativ HammerSchmidt: 9 speed 3/32
Sugino RD: 9-speed 3/32"
Sugino Messenger 3/32" or 1/8"

My LBS guy told me to use a ss chain as well even though the manufacturer tells me otherwise. Does anyone have the scoop on which to use and why? cause I am a little confused.
Thanks.