As has been said, either the ritual is important or it isn't, so how come anyone can kill stoner guy at the end and complete the ritual? And why is it so important that the five kids represent the archytypes when, one presumes, there wasn't a slut or a jock amongst the Japanese schoolgirls? And I imagine Spain/Norway etc had something different still.
I'm guessing that each area had their own "ritual" that had to happen that conformed to the archetype of what we
know about that area's monster movies. So Japan, for example, didn't have to have those different archetypes because Japanese "horror" movies aren't known for that (but they are known for children getting into the mix.) And part of the "joke" is that Japan never completes the ritual because in Japanese monster movies the humans pretty much always win and the monster is often defeated by (or with the help of) children.
This movie was more poking fun at the entire monster/horror movie genre rather than trying to be a part of it. It was sort of like the "Movie-Movie" movies only it was original instead of just being a series of scenes directly ripping off the movie(s) they're emulating.