You won't believe this, but Apple actually recommends using anti-virus software!!!
That doesn't surprise me. It's always better to be safe than sorry should the time come when it is
needed. I, for one, haven't used anything since OS 8/9; back when Norton actually supported the Mac, and made a pretty cool app suite. I highly recommended against it when there weren't any
good options available. Especially when OS X first came out, and many years after, every virus program was crap.
It's not a "fan boy" thing, it's an operating system/user base thing. For starters, those super-cool people who write viruses in their mother's secret, basement lairs want to infect millions of computers; take down banks, schools, governments, and WoW servers: most of which do not run on Apple hardware/software. You don't see any zero-day exploits for the Mac OS because no one bothers.
Secondly, the system itself is inherently
more secure than Windows, in my opinion (pre Vista). Not that Mac OS is impenetrable, but rather slightly tougher than Windows overall. Sure, there are Apple Scripts that can destroy everything, but that's kind of different. I don't want to get into all, but Windows' best solution to a huge problem was UAV (which is a horrible solution that "works").