The Unix part is definitely true. One of my professors has a Mac simply because its POSIX compliant and is designed from the ground up to work with the hardware its running on, unlike Linux.
For any kind of programming work having a *nix terminal is way better than dealing with Microsoft's primitive Command Prompt.
Its terribly unproductive though. It takes him 3 times as long to navigate to the slides/demos he shows in class as it would on Windows or KDE, since the complete lack of window management in OSX means his desktop is always cluttered.
Although, I will certainly say that most of my professors have no idea how to keep their workspace tidy (Desktop has 100 icons, have windows open from programs they were running a year ago, 8 virtual desktops all with a firefox instance running, etc...)