OK, but wouldn't the same comment also apply to gtk1, gtk2, gtk3 and many other apps that can only run with X and thus Xlibs loaded?
There is a fundamental difference: gs won't even run without Xlibs because of a dynamic library missing, while an X app can possibly run without X, to immediately abort upon not finding a screen.
This is not merely conceptual: for example, to make my printer work, I need cups, ghostscript*.tcz, AND Xlibs.tcz (not Xorg neither Xvesa nor Xprogs). The latter is only needed to supply libjpeg to gs, which is needed not as a X app, but as a filter for cups; and without Xlibs the printer won't print because of that!
So I insist that Xlibs should be in ghostscript.tcz.dep, and, similarly, in libgs.tcz.dep.
It shouldn't be included in a generic X app's dep files, because this is another matter.