That is because FBC has its own getkey function which can't be undefined - see the pulsar2d.bi (also valid for INPUT and Window). Sprite, image, font and anim can be used without p2d prefix, but I prefer the p2d for clarification.
Oh I forgot something: also to have a compatibility to the FreePascal implementation. There is no prefix but the types are p2dwindow, p2dsprite etc. So it's easier to port projects if someone wants to do that.