The Subaru Impreza STi is designed in hatchback due to its purpose. It is designed for rally. And as most people know, hatchback has less rigid body as compared to sedan. In a rally, the terrain are too uneven, unlike a circuit or track which is more smooth and flat, that's why Subaru had designed the STi into hatchback(which has a less rigid body) to suit to its purpose in rally to absorb the more shock and vibration. And as we all know, most rally cars are hatchback anyway... Audi(in the past), Peugeot, Citroen, Toyota, Ford and so on....
Subaru Impreza STi lover and owner.......