Well, the reason the number of cars in GT3 was so low was because they had to re-learn how to make the car models. Now that they've had plenty of time (and two games) to figure out how to streamline the process, GT4 will most likely have a pretty impressive selection... probably not as vast as GT2, but there'll be something for everyone I think.
To add to that further, in GT2 it took them a day or so to design a car, whereas in GT3, due to the power of the PS2, it took about a week just to make one car.
