Hosting for server admins
Once upon a time the technical sophistication required to get a "server" up and running was such that this area was limited to those who already had the technical know-how or who were willing to put in the time and resources to become systems administrators. For good or ill, that is no longer the case. Now just about anyone can have a "server" up and running on almost any box that they find lying around and, while this may have increased access to a wide range of software, it has also increased some network perils.
Much of the initial development of the web was done with Unix and the tools that were available with Unix distributions. An open variant, Linux, shares many of the tools with Unix and is very prevalent today. System administration on *nix systems has become simpler as vendors and developers have offered GUIs for system administration. OS X is an example of marrying a Unix OS to an advanced GUI.
The fly in the ointment, as it were, is MS-Windows. Windows, initially based on MS-DOS conventions, rules the desk top and has made major inroads into the server environment. Many use Windows as a server because they believe it easier to manage than other OSes. As the number of users increased many wanted to use open software tools on this proprietary platform.
However, from the standpoint of being able to offer Moodle to a population, the critical factors are that your OS has to support the building/compiling of a web server, a SQL database and PHP5. As the systems administrator it is your responsibility to manage the hardware, operating system and basic apps necessary to support your Advanced Moodle Admin.
System administrators have to be able to install and manage an operating system