If Apple launches two sizes of smartwatch simultaneously, I don’t think the positioning will centre around gender. That isn’t Apple’s style. Some men will like small watches, some women will like bigger ones. As a society, we don’t know yet what is considered socially acceptable.
When the iPhone launched in 2007, the screen was seen as overly big. In fact, Apple had to use oversized hand models to portray the iPhone as small in the marketing. By 2011, the iPhone’s 3.5 inch screen size was perceived as small.
By starting the iWatch on two sizes, Apple can effectively double its chances of correctly guessing what consumers will consider as fashionable at the beginning of the product roadmap, rather than having to adjust a few generations later.