Nah the POlO in GT5 is the 1,6 GTI 6N2.. Not the Polo 6N 1,4 16V..
Actually the Polo was not in the final version of GT2. It could only be acquired using gameshark or something. Before I knew about that, back in the days when I was playing it, I always thought it was wierd that for a brief second in the intro movie, you could see the text "Volkswagen Polo", but I could not find the Polo in the game
There are TONS of cars which we have never seen since GT2. For example a lot of tuner cars from Nismo, Mugen, TRD, TOM'S, Mazdaspeed, Mine's and Tommykaira, also Vectors, Venturis, a bunch of American muscle cars, the Delta Integrale Collezione, the Renault Espace F1, rally cars like the classic Mini Monte Carlo rally car and the Lancer Evo V rally car...the list goes on and on.
Also most cars could be race modded, sometimes into real touring cars/rally cars.
There were also road versions of the Ford GT40 and the Toyota GT-ONE. These were in GT3 also but has not been seen since.