The normal process of generating licenses for modular X packages is to run
through all source files in an editor and copy all the copyright/license info
into the license file.  However, in the case of xorg-server, there are almost
2000 source files.  We're not paid enough to do that much work in a short
period of time. ;)

Upstream has stated that MIT is a good approximation.  The only difference is
that the code will contain a large amount of explicit copyrights from the
various companies and individuals who have worked on this project.  If you're
interested, take a look at the source file of choice.