Well Gran Turismo 4 didn't launch with online play, which had been promised for quite some time.
Playing games online was a major selling point for console games from 2001 to about 2005. After that it was just expected. If you didn't have it, it hurt you.
Gran Turismo 4 also released when the talk of next gen systems hit a fever pitch. Just mere months after the release of GT4, the PS3 was unveiled at E3 in May.
GT 5 will have a much better time in America than GT 4 did. With Nascar being so close to it now....it's a given.







