Nope it's to do with weight. Each car is given a set tolerance either side of its official kerb weight which allows for the options as specified by each customer. Because the GTI model has a lower kerb weight, the tolerance levels are not sufficient to cover the increase in weight caused by the 19 inch wheels and the sunroof when combined. The R however, because it is heavier, can be purchased with these options as they do not increase the overall weight of the car by the same percentage of the original kerb weight.