Park starts for the same reason Kuyt does-he works his arse off for the team, defending from the front, winning the ball back. notice how many of the games he starts against tough opposition, when manu can't just roll them over.
and yes, Fergie will start Rooney, because the instant he doesn't he'll have every fan and englishman after his balls. rooney is the best forward in the world, AND he's english.