Defining Apocalypse or Apocalyptic

Mark Goodacre pokes a bit of fun at a oft-used definition of apocalypse here. Although the point Goodacre makes is interesting, I think that there are more serious methodological challenges based on how the definition was developed (descriptively) and how it is often used (prescriptively). That is, the definition appears to be developed from certain literature that one already determined was apocalyptic and then taking that very same definition and saying see these books are apocalyptic or that apocalyptic literature has to be characterized in this particular way.