I have no idea why for any reason the air frame would need extra fins other than that it looks cool in the eyes of the designer.
Pretty much. There's a reason why they're game designers and not aero engineers.
Frankly I don't understand the recent gaming trend of trying to have cool planes in everything when sticking in an F-16 will do just about as well - and I'm not even talking about flight sims, I'm talking freakin' first or third person shooters like the aforementioned Just Cause. Even Ace Combat, the game that started it all, moved away from this with Assault Horizon.