In assisting ISD's with their own Moodle server, am always recommending Community Enterprise OS (CentOS). Several reasons ... major one ... getting updates to the pieces that make up an AMP (Apache, MySQL, PHP) server. Yes, Moodle/Joomla's could be run on Windows, but why would you want to? AMP is NOT updated by MS. Matter of fact, there is only ONE company in the world that claims to provide updates for AMP on the Windows platfrom and it's not free.
Is updating really that easy? Well, how about this simple command: yum -y update [ENTER].
There are some that still have the mindset that ALL must match ... looking at Ubuntu desktops, then one must have Ubuntu Server. That might be true IF one is using local lan apps, but for a Moodle/Joomla server, it's not necessary. Moodle and Joomla just needs to talk LDAP.
In some cases, it's not a bad idea to have a public facing server to be of a different flavor than what you are running inside.
Just my 2 cents, of course ...
http://www.centos.org/