Leave the pretties to the artists. Not developers.
/usr/local or /opt
Don't quite get your point, NWN & UT2004 work perfectly across any distro. They come as a complete package and expect to find nothing more than a value stuffed into $HOME.
However, you do end up losing out on the advantage of common libraries like this. But, it's easily fixed.....
Each distro should hold a file in /etc called something like 'locations' (or whatever) and list where an installer is expected to install the appropriate files.
Likewise, have a common db that local installs can list what files they use, so the package manager can check it's own db (regardless of format) and the 'local install' db to see what files are loose. It would be simple to write a script to handle the install of ANY software then.
I admit some distros do funny things with certain config file locations, but most commercial software shouldn't be touching these config files any way (but, can also be resolved by above method).
Never seen an update for UT2004 for upgraded Libc, and it still works (he says after not playing it for some time, but meh - never seen an issue like that). So I'm guessing it shouldn't be a huge problem. I am willing to stand corrected here as I am nowhere near being an expert on libc.
Kernel modules suffer from it though. - So, thinking about it, provided the libraries are 'static' to the program and aren't anything to do with the system you really should be fine (MS _probably/may_ still use the same compiler+faults from years ago).
How about MS (that's Mark, not Micro) puts some effort into making pretty frontends to stuff like firewalls etc that work on X, and NOT KDE/GNOME. I like the layout of UDE (I would recommend to people who like *different*), therefore don't want all the KDE/GNOME base stuff installed. Autologin for xdm? available for kdm and gdm, but could do with being on all home systems I feel.