http://www.dailymail.co.uk/pages/live/articles/news/news.html?in_article_id=467781&in_page_id=1770&ito=1595 - Why women drive with two hands and men with only one
"It's also why men drive with one hand on the steering wheel. They are physically relaxed as they think the car is part of them.
"Women drive with two hands because they see the car as more 'detached'."
How about it's just safer?