Look, unless you're a mindless zealot, you realize that the software license costs are only the beginning of your costs. Linux administration ain't cheap.
A unix admin can watch far more servers than a windows admin can (though that gap is narrowing from NT->2K->2K3). That and the fact vmware itself will reduce the load on admins and I doubt they are spending a whole lot more..
Most IT consulting companies will charge about 1.2 to 1.3 times as much for a Unix Admin as a windows admin but Ive seen companies apply less than an FTE to maintain about twenty *nix servers..