...no the old saying a pro gets paid isn't the real reason, i know a few "Uncle Bobs" who get some pocket change for weekend weddings
The primary distinction (right now); the working pro can get that shot day in and day out consistently, whereas the amateur from novice to advanced enthusiast will probably hit it once in awhile. As i've said before; the camera is just a tool and nothing more, it's the person behind that view finder that determines the final image and the working pro gets it more often then the non-pro.