Fingernails grow two to three times faster than toenails. A fingernail replaces itself in about six months while a toenail takes a year.
Feet are farthest afield in the circulatory scheme of things. A better blood supply to the fingers keeps them chugging along at a faster clip. Nails are basically protective and since our fingers are busier than our toes, they are more likely to need replacing. Also, constant exposure to sun and air may aid their growth. Feet are locked up in shoes most of the time.