However, I suppose there is more to it than that. The issue is that the fact OSX is Unix under the hood is merely an implementation detail and always has been. I'd much prefer it if Apple used a solid, up to date Linux distro under the hood, but they don't. To me using the Unix system in OSX feels a bit like using Cygwin on Windows.
Conversely with modern virtualisation software, you can have your cake and eat it. I use OSX to run desktop and media apps, at which it excels, and have Linux and Windows 7 running in VMs. Perhaps not good enough if you're doing resource intensive stuff like heavy duty compiles on your Linux system, but for my purposes it works very well. It has the added advantage that if I hack around with the VMs and something goes wrong, I can usually revert to a recent VM checkpoint.