The version of perl (or apache or mysql) that comes with the OS should be used solely by the OS.

There's no distinct line between OS- and non-OS-stuff in RedHat; /usr/local/bin is there only because it's supposed to be there; all app stuff is jammed into /usr invariably. Is OpenOffice as shipped by RH meant to be used by the system only? Where does a RedHat system need mysql?

The reason RH still ships Perl 5.8.0 (patched heavily) with their OS is because their scripts work with 5.8.0 and upgrading may break that.

Mind to provide anything to prove that? If "their scripts" only work with a patched perl and might break with a perl release change, they are poorly written in the first place. But then, their OS related scripts are written in python. It is possible to de-select perl upon install, but it will be installed anyways because of bogus package dependencies.

Let's have a look. Where does RH's systems rely on perl? As of a RHEL-4 update 7 default install (which ships 5.8.5, btw)

[shmem@rhel4 ~]$ for pkg in `rpm -q --whatrequires perl | grep -v perl
+`; do rpm -ql $pkg | xargs perl -nle 'exit if -d $ARGV[0];/\bperl\b/ 
+and print $ARGV and exit' ; done
/usr/bin/genkey
/usr/bin/foomatic-compiledb
/usr/share/foomatic/db/source/printer/NEC-PinWriter_P6_plus.xml
/usr/bin/decode-dimms.pl
/usr/bin/fileshareset
/usr/share/mimelnk/application/x-perl-module.desktop
/usr/X11R6/bin/xscreensaver-getimage-file
[shmem@rhel4 ~]$
[download]

the only script "(C)RedHat" is /usr/bin/genkey of crypto-utils which is fairly old and doesn't rely on any esoteric perl configure settings or patches, and

[shmem@rhel4 ~]$ rpm -q --whatrequires crypto-utils
no package requires crypto-utils
[shmem@rhel4 ~]$ su -
Password: 
[root@rhel4 ~]$ rpm -e crypto-utils
[root@rhel4 ~]$
[download]

not even that one is needed by the system. I have not checked, but I suspect the dependency on perl of any later RH OS to be even less.