Thought is that you should wear a watch on your non-dominant arm (which I don't agree with but that is the thought); so left handed people would wear their watch on the right hand.
So a left-handed watch would have the crown on the left side of the watch because the 'crown should point towards the persons fingers'.
And yes, there a lot of watches sold that offer the crown on the left side of the case, rather than the more common right side.
