@BlogZbod... It's perfectly possible that the asymmetry at the front means that the air on the LHS of the car is somehow moving quicker than the air on the RHS. Therefore, by having the exhaust exiting rightwards, it accellerates the air on that side.... It could also be that because this is a clockwise circuit, that they believe this will help them go round right hand corners.... (a la indycars)....
My suspicion is that it's much simpler than that; if it exits in a straight line, it will set the rear wing pylon on fire, and we say bye bye to the rear wing!