the difference is most events do their setup BEFORE in ongoings. Snyder is just starting from square zero, for the most part.
but even then, most high concept events have the high concept immediately then get straight to the action in the first issue
House of M>mutants control the Earth!
Annihilation>Annihilus is here and he's pissed!
Civil War>heroes are fighting!
Siege>Norman Osborn is attacking Asgard!
Blackest Night>Black Lantern zombies!
Fear Itself>everyone gets a hammer!
Flashpoint>Flash went back in time and fucked everything up!
AvX>Phoenix is here and people disagree whether that's good or bad!
Forever Evil>Crime Syndicate!
Civil War 2>Minority Report!
Secret Empire>Evil Cap!
except Metal (and Civil War II) took a third of its story to get to the main concept of the event.
and events with more complex concepts like Final Crisis and Secret Wars don't waste time on exposition, showing the "status quo," so to speak, through action.