I think thats how they did it in the series, but (correct me if I'm wrong, anyone) I think this game wants to focus more on using reflective surfaces as portals as a part of its theme. Besides, that would kinda throw NBen into the action too soon, since he just said he would need to delay his full participation until he gets back from his work. I think (just my opinion, at least) we need just as much interaction in the Real World as we do the Mirrored World. Maybe the characters still in Inaba could start seeing and dealing with some of the darker effects of the gateway opening in the mine, perhaps noticing a sudden spike in crime or inclement weather or wild animals, maybe being attacked by evil-influenced humans or something? Would have to clear it with Vergil, of course, but *shrugs* just a thought.