"With sidescrollers, developers can simply separate the background and foreground layers and distance them apart," the Vblank post reads. "However, with a top down perspective using cube-like objects such as buildings and vehicles, it would require the graphics to all be recreated as 3D objects, a new rendering engine, a camera system that players would be happy with, and further optimizations. For a new game it would be more feasible, but for an existing one, it simply would've taken too long."
Retro City Rampage for 3DS, which includes the most recent version of the game with enhanced graphics, was announced yesterday. The 3DS port will be playable at Nintendo's PAX Prime booth next weekend.