An interesting thought...that the "Roanoke" mentioned in Sellers might actually have related to one of the NC locations. Bears consideration. Have you ever run across any Richardson in either of these places?
On the other hand if Roanoke Co., VA was established in 1838 out of Botetourt and Montgomery counties, it's possible that when Sellers (or his source) referred to Roanoke in VA he was referring to the COUNTY not the CITY. Though I don't have exact birth dates for William and "King" John, they both would likely been born after 1838 when Roanoke Co., VA was established.