mangos is the union of a core and a database (and .dbc, that are extracted from the client), so it's impossible to hard code every part of the game in the c++ source (no, is possible but not very intelligient) so there are some abilities that need a script or other that are treated "generally".
so, for exemple, the scripting of battlegounds of arenas are done in the code, as some exeption like raise dead ecc, other things like the proc system, the bonus that spells take are taken from database.
there are so many thing to say that probably a dev or a smarter mangos user than me can say them better....
Happy mangos