How come in England, Wales and Scotland, ladies had different names than men?

For example, men had the name Griffing and women were known as Griffin. Although I've checked, and there are men with the last name Griffin at that period in time, too. We have a Griffin crest of arms over the mantle at my uncle's house, so how can this be? I've seen my family tree and women are named Griffin and the men are named Griffing and my Uncle decended from one of the women named Griffin. When these people come to the USA, or at least after the 1700's, this name changing stops!