It's not missing on my system.
I can see that it is hard to believe, as it is something rather obvious when all "/usr/lib/*.so" files are missing from such an important TCZ file. Nevertheless I've redone my tests with QEMU (e.g. v0.11.1), VirtualBox (e.g. v4.2.16) and used the "7-Zip File Manager" (all on a Win7 x64 host) to browse the ISO and the contained 'Xlib.tcz' file. But as my earlier observation still stands, I can only conclude that I've got some faulty downloads.
For comparison here are my MD5 checksums for the ISO files in question:
with the first one containing a 'Xlib.tcz' (i.e. 'f1d1507e66a1c5ad6f7ac17c4776f779') that still contains the shared libraries in question, and the two latter ones containing a 'Xlib.tcz' (i.e. 'c66b89774b6ba0071fc3f4b9551f075c') where those file have "vanished".