The odd part is you're acting like linux isn't inherently secure. While I will grant you, it isn't perfect out of the box, a small amount of configuration can make it very secure for your needs.
You're not dealing with Windows here, where it constantly needs to check in, in order to know what the hell is going on. I would recommend a secure setup of LDAP for account information (pick your openldap flavor, Fedora Directory Server works great here), and a kerberos server for passwords.
I would also like to point out the "commercial" Red Hat Satellite server, or the open/free Spacewalk server to manage all servers at once, like you can do with AD.
Factorials were someone's attempt to make math LOOK exciting.