This is a known "feature" of the WoW resolution detecting code. The reason why it works in when you select the X24WG-NAGA is that tells Windows about two higher resolution modes (1920x1200 and 1280x1024) in a form that the resolution detection code in WoW can handle.

All the file does is add these two modelines, an ICM profile (which is pretty much worthless for an LCD like this), set the maximum resolution, and provide the model name. The only thing a X24WG-1080P option would do differently is give the model name "X24WG-1080P" instead of "X24WG-NAGA".