I think the big selling point for macs among the hacker community is that it's Unix, but without the hassles of Linux.

If you find yourself asking why Unix over Windows, it's really because the dev tools and the command line environment it offers are much more powerful. I recommend starting with Linux. Play around with it for a few months, learn as much as possible, you'll be pleasantly surprised. The get a mac cuz it's a million times more convenient and polished.