Obviously you haven't been around since the beginning. The first three Grand Turismo titles were all released within 6 years of each other. With each game being a marked improvement over the last. With GT3 A-Spec arguably being the best of the franchise.
Grand Turismo released 1997
Grand Turismo 2 released 1999
Grand Turismo 3 A-Spec released 2001
Grand Turismo 4 released 2005
Grand Turismo 5 released 2010
I played 3 up until the day 4 came out. The jump in quality between 3 and 4 was so drastic and the fact that nothing on the market could compare to 4 made the 4 year development time feel justified.
But to say that a five year development time is justified when they pump out a game on par with the competition is absurd and frankly a waste of resources. I was expecting GT5 to be head and shoulders above any other racing game on the market simulation or arcade.