Xorg-7.5-dev.tcz provides the development part of about 15 libs that are provided with Xorg-7.5-lib.tcz, so my assumption was that the -dev can't be very useful without -lib. And since -lib has no further dependencies, I can't see a downside, since sizes are: Xorg-7.5-dev.tcz = 1.8MB, Xorg-7.5-dev.tcz + Xorg-7.5-lib.tcz = 2MB. It just prevents that some X libs will not be compiled in statically "by accident".