Macs (i)n Movies

I know Macs are quite the favorites to all video-editors but what I don't get (not that I don't support) is that every movie (almost) seems to use nothing but a mac in any scene that even remotely involves a computer. A scene with a personal computer? It's gotta be a Mac!

Though I'm comforted by the fact that you don't see any windows boxes in movies, is there an unspoken rule?

How about some GNU/Linux while you are at it...