I'll go further than that, I'll get off at the depot. Why not get a mainframe? Afterall, do you hear about home users having trouble with a virus on their mainframe? And with 70% of the lines of code in the world written in COBOL, it's obviously got more software than anything and the de facto standard for software.
Seriously, though, with OS X being built upon BSD, the security model is going to be inherently better at a base level than the Win.* model, which is based on slapping things together. I know that any computer system that is connected to a network is going to have risks and issues. However, there is such a thing as degree of difficulty. It is true that the WinNT core/kernel/etc is based on the work of Dave Cutler, who was a key player in the development of VMS. However, per the culture of MS, a lot of slapdash work has been done along the way and, in the name of backwards compatibility, has been fixed in the nature of spit-and-bailing-wire.
OS X may have its issues (I own Macs and I admit that they aren't perfect), but good gravy, the comparisons speak for themselves. If the big money places (banks, corporations, governments) use a lot of *nix and mainframe servers, wouldn't that be the best target for the black hats? Recall the John Dillinger line, when someone asked him why he robbed banks: "Because that's where the money is." Okay, so why aren't Linux, Solaris, Oracle, DB/2, etc, breached far less often than Windows? Perhaps there is something inherently less secure in Windows ...