Good point. I didn't even think of the practical implications. Also, you can place GUI elements outside of the arena, so it don't obscures the action.
If the borders were a part of the gameplay, something physical you can bumb into, then it makes sense to let it be a visible in-game element rather than just the monitor edge.
I tried splitting Resistance is Fruitile up, so that the play area is to the left, with the non-playarea stuff marked with red. It really take up alot of screen area! Might be worth it, but it's really a bold design decision.
