I have just been looking at the front end of the McLaren and the Ferrari there are some obvious differences. Ferrari appear to have gone for a higher mount of the suspension parts, which means the drop nose they have, but they have a very thin nose to the car creating a large gap underneath to the floor. The McLaren doesn't have this gap creating a lower profile nose.
I would guess that this is to do with the flow of air under the car. Ferrari are trying to control it and push more air under there so relying on the floor (which appear to be set back) to create a large amount of downforce. McLaren appear to be trying to limit the flow of air under the car so must be relying on other devices to create their downforce elsewhere. A cas of swings and roundabouts, just really a question of whose answer is the most efficient in race terms. Though there is something about the step down to the drop nose rather than the nice clean lines of the McLaren that doesn't appear to be that aerodynamically efficient, the flat step must produce some fairly large interference with the natural flow of the air?