OS X most definitely is a Unix
OS X most definitely is a Unix. It happens to be my personal favorite desktop *nix. I wouldn’t pay the premium to use it as a server, but for the desktop, it’s hard to beat.
I think you proved the point, with your comment about the AS400 & the bank mainframe. Joe Schmoes run Windows. Big companies with valuable information run AS400s. Banks have mainframes that *define* what money is. Sure, you may infect a greater quantity of machines by targeting Windows, but if you had a purpose — such as espionage, wanting to make money, revenge, general malice, etc. — it would make much more sense to target something valuable, like an AS400 or a bank mainframe. Windows may be the bigger target, but it has never been the more valuable one. And, given that the source code for Windows has never been *officially* released, it is certainly the harder target. Why would it continue to be targeted, almost exclusively, despite all of these reasons?
On a tangent, modern AS400s now run… Linux. 