Why can't I use XeLaTeX instead of pdflatex on Fedora or RHEL 6?

When trying to use XeLaTeX, you may get a message like:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! You are attempting to make a LaTeX format from a source file
! That is more than five years old.
!
! If you enter to scroll past this message then the format
! will be built, but please consider obtaining newer source files
! before continuing to build LaTeX.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

! LaTeX source files more than 5 years old!.
l.545 ...aTeX source files more than 5 years old!}

?
! Emergency stop.
l.545 ...aTeX source files more than 5 years old!}

No pages of output.
Transcript written on xelatex.log.
Error: `xetex -ini -jobname=xelatex -progname=xelatex -etex xelatex.ini' failed

###############################################################################
fmtutil: Error! Not all formats have been built successfully.
Visit the log files in directory
/var/lib/texmf/web2c
for details.
###############################################################################

This is a summary of all `failed' messages and warnings:
`xetex -ini -jobname=xelatex -progname=xelatex -etex xelatex.ini' failed

This is confirmed to be a problem on CentOS 6, Scientific Linux 6, Red Hat Enterprise Linux 6, and Fedora Core 13.

You can correct this issue (as root) by:

cd /usr/var/texmf/web2c
xetex -ini -jobname=xelatex -progname=xelatex -etex xelatex.ini

Once you type this you will get the same message, but have the option to press return and generate the file anyway.