its a combination of both car and driver. If schuey was put in a Mclaren he would probably still win, but not by as much.
Look at it this way, some people say its the car that makes schuey win, but if it was only the car why does he get 1-2 seconds a lap on barichello if barichello drives exactly the same car.
The same thing work for people who say that he is the guy winning, not the car. If he was in a jag or a minardi i doubt even he could win.
In conclusion, i think its just the combination of both the best driver and car...