If there's a reason for Porsche not wanting their cars in GT5 would probably due to the fact that PD is closely associated with Nissan, especially with the development of Porsche's biggest nemesis the GT-R. Already Porsche have accused Nissan of fabricating GT-R's times at Nordschliefe and I wouldn't be surprised if Porsche would invoke that that there's a definite conflict of interest when it comes to PD and Nissan. If this was the case it's too bad because if there's an epic showdown in GT5, it's definiteyl between the 911 GT3 and the V-Spec GT-R.