Different engine, sure... but they're trying to replicate IE as best as possible.
Different engine; you're right in that I doubt there will be much problem with screen edge scrolling, but its a fairly crappy solution for 2014. Direct dragging with the mouse cursor would be best, but I'm not sure if there are re-draw issues with Unity-generated graphics when zoomed in. This could make the game choppy on some machines.
Why is this a crappy solution in 2014? Because all other games in 2014 have fixed cameras on their PC and thus scrolling is made extra difficult, since usually the camera is locked on them? If so, that's not a very good reason IMO.
While dragging with the mouse seems reasonable (and I assume will be in) I have no reason not to believe simple mouse scrolling like in the BG's would feel absolutely fine in PE, rather than in other modern game with their PC-locked cameras.