Could some one please explain the following to me:

There are two sub-styles of (genuine) pils: German Pilsner and Bohemian Pilsener. Notice the spellings, pilsner and pilsener. I'd be less inclinded to say "Please explain" if it weren't for the classic czech beer, Pilsner Urquell.

(There are lots of lagers that imitate the Bohemian original, however, I don't count all those lagers as pilsner. I don't even count classic american "pilsner" as pilsner.)