You stated that Unix had more overhead. It doesn't, either from a hardware standpoint, or an admin standpoint.
A number of studies have concluded that UNIX requires 2-3 times the admin support costs, and you cannot possibly think that UNIX servers and the UNIX environmentis not far more costly. Of course, Linux has changed the scene, such that low end print and web servers are next to nothing in cost, but Linux isn't figured in the historical costs on UNIX.