Question of the day

Why are “mail fraud” and “wire fraud” different charges? Why isn’t there just “fraud”, regardless of the medium used for it? Likewise, why is “vehicular homicide” different from plain “homicide” or “manslaughter”? Does the medium used really change the severity or importance of a crime? Aren’t there already degrees of crimes (such as the difference between 1st degree murder and manslaughter)? Why would the medium used change the act that was committed?