Time to bring back again the (true) story of when I was working at uni and they were looking for another graphic designer to join our team. Boss told us one of the candidates refused to do the test because the computer didn't have Photoshop installed. All they needed to do with an image editor was to crop an image.

I really think most people use Photoshop for the same reason they use Windows - they don't really know/they don't want to learn anything else.