Terminology has certainly morphed over the years. "English" tobaccos, as MSO said, used to mean tobaccos without a significant flavoring, but over the years, it came to mean blends with Latakia, probably due to the popularity of 965, Nightcap, and the like. "Balkan" wasn't even a term back when I started out (in the 70s), "Aromatic" was a term that often included Latakia blends, but has changed over time to mean a flavored tobacco. "Cavendish" used to mean either a toasted tobacco, or ones that had been flavored, pressed, slice, and tumbled out, but now companies will use the term for flavored tobacco. Basically, pipe terminology is decided upon by common usage and the influence of the marketers of the manufacturers.
Russ