That is a really good question Mark and not something I have really thought about so here are my thoughts.
Since I was a lad I have always loved looking at photos sometimes just enjoying the picture other times trying to visualise the memories people have.
My grandad had a Zenith E SLR which I was really fascinated by when I was 14 and he occassionally would let me take a picture with it when I was on holiday, saddly he died a few months later and I inherrited the camera and enjoyed taking photos with it, when I turned 18 I bought an OM-20 which I used a lot and I have fond memories of me and a friend who also had an OM-20 going places and comparing shots (he is a pro now).
In 2001 I bought my first Digital and loved it, it re-awoke the SLR facination in me I just love to capture memories, put together books so people can re-live the event. It is also about trying to capture the amazing natural moments that occur every day every time I look out of the window I am constantly looking at every detail of my surroundings to see what would make an interisting picture.
I have also rebelled along the way usually when my wife tries to get me to make a living out of it, for me it is a hobby almost an escape so I think like others here because I can't draw or paint it is a way of expressing myself artisticly, it is something I am passionete and protective of and I do not want to spoil it by trying to get comercial.
I also find it helps me enjoy my surroundings more whether it is in the country, urban or even a social event by looking for images I seem to get far more out of it.
Originally it was more about preserving and capturing memories but in the last year it has also been about art and interacting with other like minded people such as yourselve's.
Hopefully all that will make some sense