You keep saying this, but it simply is not true, and you have no evidence to back it up. All that Elvis has come up with is some quote translated from Japanese to German to English suggesting that GT5 has had 150 people working on it since 2004 when it hasn't.
You keep dodging my question, where did Tourist Trophy and its 140 or so bikes come from, out of thin air? Why if they were working on it since before GT4 was released did GTHD only have 5 cars, 1 track, and a GT4 game engine? Why did Prologue use the GT4 game engine? None of what you say makes any sense. There were no PC based PS3 devkits in 2004, certainly no Cell based devkits, I don't even think that IBM had operational simulators/emulators in 2004. So what were they implementing before GT4s release? You could say that they were modelling the cars, but the modellers were busy building 140 or so motorbikes. GT PSP was announced in 2004 also, so some of the programmers would have started to work on that.
What you are saying makes absolutely no sense.