The difference is subtle, and may end up being exactly the same behind the scenes.  With the first approach (min version required > 6.1), the code path would only be enabled if you defined the base supported iOS SDK to be 7.0 or greater in the project settings (currently 6.0).  In this case, even if you were building the project in Xcode 5, if you didn't change the base SDK of the project, this code would not be enabled.

If you only check for the presence of the iOS 7 SDK, however, this code path would be triggered in any development environment which has the iOS 7 SDK installed, i.e. in Xcode 5 in this case...just by virtue of building it in Xcode 5.

Theoretically, you could build the project in Xcode 5 and still keep a minimum version of iOS 6.  In practice, though, I don't know what happens at runtime when you try to run that app on an iOS 6 device.  That's probably worth finding out, before committing this change.  I'll take a look.