I can only hope Blizzard will follow Valve.
this list to make S3TC available for Linux (so distros will be able to provide s3tc package out-of-the-box) or simply allow everyone use it (this make possible include S3TC into Mesa).
The other solution for S3TC problem is S2TC, that is already available in Debian and Ubuntu. When you install psychonauts-bin:i386 from Ubuntu Software Center you will also get libtxc-dxtn-s2tc0:i386 installed. So isn't solution is already here?