I got curious about this so did a little research and came up with the following reasons:
- It shows both hands clearly ie. one hand doesn't cover the other.
- If the watch has a date function the hands won't hide it. The date function is usually found in the 3 or 6 o'clock position.
- The hands form a smile shape when at 10:10 as opposed to a frown if they where placed the other way (I'm not so sure about this one!). If this is true it was definitely someone from the marketing department who came up with this!
- The hands will frame the watch makers logo and not hide it.
- It looks good! Having the hands in this position is pleasing to the eye and looks better than having the hands form a straight line if the time was 9:15 or something similar.
I guess as well as all of the above reasons photographing watches at this time has become somewhat of a tradition and industry standard.
So there you have it, my not so scientific explanation of the 10:10 mystery. If you know of any other reasons or if you have any of your own ideas then post them in the comments.